The Potency of Ungovernable Impulses

The Investigations of Mossa and Pleiti #3

by Malka Ann Older

A brand-new entry in the Hugo, Nebula, and Ignyte Award-nominated sapphic, cozy space-opera mystery series The Investigations of Mossa and Pleiti, which Charlie Jane Anders calls "an utter triumph."

When a former classmate begs Pleiti for help on behalf of her cousin—who’s up for a prestigious academic position at a rival Jovian university but has been accused of plagiarism on the eve of her defense—Pleiti agrees to investigate the matter.

Even if she has to do it without Mossa, her partner in more ways than one. Even if she’s still reeling from Mossa’s sudden isolation and bewildering rejection.

Yet what appears to be a case of an attempted reputational smearing devolves into something decidedly more dangerous—and possibly deadly.

“The mystery will enthrall those looking for more sci-fi/mystery blends, while Mossa and Pleiti’s relationship is a delight for sapphic romance readers.”—Library Journal

Genres: Mystery, Science Fiction, Queer, Fiction, LGBT, Audiobook, Mystery Thriller

243 pages, Hardcover

First published June 10, 2025

Reviews

[EveStar91 · Rating 4 out of 5]

That is, I regret it now; but when I probe the gallimaufry of blurred memories from that night I can still feel the potency of the ungovernable impulse that demanded I place my palms on her bony shoulders, the elation of pouring my strength into the shove, of feeling her weight and solidity shocked backwards by my hand.

The third book in The Investigations of Mossa and Pleiti series, The Potency of Ungovernable Impulses sees Pleiti flex her recently uncovered investigating skills by herself to help out her friend at another university, in the process acquiring a new respect for the Modernist stream of studies, making new friends and renewing old friendships, and solving the mystery with some good old fashioned skills; all while Pleiti and Mossa try to navigate their growing relationship, dealing with their insecurites and learning to work their way to each other.

This book is a great addition to the series in terms of both the world-building and the characters. We see more of the world Giant, as well as a bit of its history and prejudices. It's interesting, to say the least, but perhaps not surprising, to see the tensions that can arise in academia even in a futuristic space settlement society. The plot is slow at first - with the characters mostly reacting to events, but Pleiti steadily makes headway in trying to solve the mystery alone before Mossa joins her, very reminiscent of the plot in The Hound of the Baskervilles. How they each work towards solving the mystery and rationally finding the culprit is a good reflection of their individual temperaments.

Both Pleiti and Mossa grow as characters; Pleiti with her perception of academia and scholars, Mossa with her introspection on the kinds of cases she wants to take up. They also continue to explore their relationship after some angst and more open conversation, especially regarding mental health. While it was good to see them actually talk to each other about their feelings and expectations, the angst and insecurity felt a little off-key when looking at how their relationship grew in the previous two books.

A special note must be made of the author's incredible linguistic skills in envisioning a close knit society comprising people of multiple nationalities and cultures starting from scratch as a new society. It is truly refreshing to see this melding of languages and speech patterns (and food items too), seen even in the first two books (Book 2 review), as opposed to simply including some stereotypes bordering on (or invading) blatant racism and calling it representation. However, not knowing these languages don't really stop the flow as a lot can be gleaned from context. As a person who's interested in etymology and linguistics, I enjoyed tracing the various words with roots from different languages, and of course also looking up new foodstuffs. Gallimaufry, if you were wondering, means a confused jumble or medley of things - its origin is old French, but it is actually an English word (ref. Oxford dictionary).

This book, and series, is recommended to anyone who might enjoy a Holmes and Watson kind of mystery in a Sci-Fi world, with female lead characters and a sapphic romance.

The Investigations of Mossa and Pleiti series:
Book 1: The Mimicking of Known Successes
Book 2: The Imposition of Unnecessary Obstacles

Thanks to NetGalley, Tor Publishing Group and the author Malka Ann Older for an ARC of the book, the review is entirely honest.

🌟🌟🌟🌟1/4🌟
[3/4 star for the premise and the whole book; 3/4 star for the characters and their growth; 3/4 star for the story and themes; One star for the world-building; One star for the writing - 4 1/4 stars in total, rounded down to 4 stars.]

[Mara · Rating 5 out of 5]

4.5 Stars - This is the best book in the series so far, IMO! A clear homage to The Hound of the Baskervilles, this investigation not only delivered on plot, but also significantly deepened the dynamic between Mossa & Pleiti. Before, I didn't totally understand what went wrong with them the first time around, but now.... yeah. I see it :)
Just a great example of a sci fi romantic whodunnit!

[Bethany (Beautifully Bookish Bethany) · Rating 5 out of 5]

4.5 stars rounded up

I love this series and will always read them!! Sci-fi mysteries with a sapphic Watson/Holmes dynamic that's super academic? Sign me up! This is the third installment, and Pleiti is taking the lead. A friend from another university is concerned about threats to her cousin who is up for a big promotion in her academic department. Mossa is dealing with a depressive episode and Pleiti does her best to unravel the mystery on her own. But things might be more dangerous than she bargained for...

The mystery is great and it's fun to see more of this world set on a colonized Jupiter, but I also love how it's dealing with mental health issues in the context of a romantic relationship. I've always said the use of language is a really cool part of the world-building, and I stand by that. Older uses a mix of English and terms from other languages (especially Spanish), imagining a diasporic future where peoples and languages have mixed. This might not be something everyone enjoys, but I don't mind either looking something up or figuring it out via context clues. I think it creates a strong sense of place and culture. Anyway this was great and I want more! I received a copy of this book for review via NetGalley, all opinions are my own.

[Rachel (TheShadesofOrange) · Rating 4 out of 5]

3.5 Stars
This was another enjoyable entry in this science fiction mystery series. I enjoy the loose Holmesism inspiration.

I enjoyed this newest edition but am also unsure if this newest installment added to the series. I enjoy the premise of the series but there isn't necessarily enough compelling forward motion of the plot to keep me coming back for more.

I would recommend this series for anyone looking for a good sci fi mystery. You could jump into this volume but you'd likely want to start at the beginning to follow the character development in order.

Disclaimer I received a copy of this book from the publisher.

[Chantaal · Rating 4 out of 5]

This series continues to be a comfort read series for me, and though I didn't enjoy this entry quite as much as the first two, it's still enjoyable and lovely to be in this world with Mossa and Pleiti.

In this third novel, we follow along with Pleiti as she helps an old school friend with a mystery at a different university where they are being targeted by an unknown person who hates them for unknown reasons. Why not Mossa and Pleiti? Well...we get an idea of why they fell out the first time they were together in school, and we get to see them try to figure out why and how they've hurt each other and do their best to work through it.

The mystery itself is pretty solid, but this book feels more like it's about Pleiti and her inner workings versus the mystery itself. The big reveal felt underwhelming, but that played second place to Mossa and Pleiti figuring their shit out.

One thing I do have to say and I've seen it mentioned in both positive and negative lights in other reviews, is that there is a lot of use of "slang" terms that have been adapted and evolved for this future time. I don't recall these terms being used so heavily in the first two books the way they are in this one. While I don't mind it, I do wish we'd had more of it in the first two books so that it didn't feel as jarring in this one.

The little wink at the Holmes canon at the end of this book was lovely.

Again, while I personally like this the least of all three books so far, that's like saying books 1 and 2 were 4.5/5 stars and book 3 is only 4 stars. They're still fantastic reads set in a world that I love being in.

Many thanks to NetGalley and Tor Books for the ARC! The Potency of Ungovernable Impulses is available now.

[carol. · Rating 3 out of 5]

The first book of a series is always going to leave world-building questions (unless you are Brandon Sanderson), and subsequent books are when the author gets to enlarge their scope and start showing how pieces fit together. When Older gets a chance to do this, she focuses on the anthropology of the society rather than the science of the world. This, I think, belongs to a category I think of as sci-fi light. I don’t even mean Star Trek-light, I mean lite as in less dense (perhaps fitting since it is set on Jupiter, a planet less dense than Earth). To contextualize, it is the Becky Chambers school of sci-fi; focused on relationships, with world-building that is more creative or parallel than forward. Much like the low calorie version, I find Older’s work sweet, but not particularly fulfilling.

This story continues to take place in the circumscribed universe of academia, and it is easy to imagine analogues to current Earth colleges. It begins when a Modernist (a term used with derision by some) colleague, Petanj, arrives from another campus requesting help. Her brilliant cousin is being targeted by a vicious smear campaign that has threatened to become physical. Mossa is deep in a depressive fugue when Pleiti reaches out, so Pleiti takes on the challenge solo. As events become more serious, she starts sending telegraphs to keep Mossa apprised.

Pleiti represents the Classical (Earth-focused) department of academia, and Petanj the Modernist, a rivalry that sounds more than a little esoteric. However, Older uses it to flesh out different methods of coping with planetary exile. This is an interesting idea–think, to take an example completely at random, of the academic idea of diversity in inclusiveness versus a more preservationist view. Unfortunately, at some points Pleiti’s narration becomes more of a an internal wondering than thoughtful contextual dialogue.

We get a touch more science in this installment as it relates to oxygen supplementation and air purifying: “Atmoscarfs are not, strictly speaking, necessary for survival in Modern times. The atmoshields around each platform provide necessary levels of oxygen, as well as minimum temperature. But these basic conditions are far from ideal.” I appreciated the way this all manifested within the story, with ramifications to clothing and social signifiers. It didn’t go as far as I was hoping.

What I appreciated less were the random Earth-isms, or words/stems left over from Earther language. I definitely didn’t remember these linguistic gymnastics in the first book, and I was struck how these academics were supposed to be publishing professionals and yet sounded like they were trying to be hip teenagers (‘grok'? Really??). I didn’t appreciate it because it felt awkward and inserted (of course any language this far in the future won’t be standard English. We get it. It’s one of the understood assumptions in literature that we are not trying to account for linguistic shifts). The words drew on a wide variety of languages, and I felt like it was done awkwardly, interrupting the story. When I read the About the Author, I learned Older is “the executive director of Global Voices, a community of writers, editors, and translators… advocating for indigenous and minority languages.” Ah; it begins to make sense, although staying with Spanish, French, and Hindi seems contradictory. This is very much one of those YMMV situations; personally, I think Older’s circumvention of sci-fi conventions (use new, not old) didn’t bring much to the table.

“‘Dafuq?’ I asked, wondering what I had missed.”

The draw to this book–and the series in general, I think–is emotion of the relationship between Pleiti and Mossa. It takes it far beyond the simple ‘Holmes and Watson on Jupiter’ premise. It is a challenging relationship, although Pleiti tends to be very dramatic about it.

“I was doing no good here, and if I was with Mossa… well, I might not do any good there, either, but at least I wouldn’t be constantly concertina’d inside by this awful, inescapable longing; the crumbling conviction that I had mad a terrible error in leaving and must, at all costs, undo it.”

As the third in a series, I think it could stand alone. However, while the mystery certainly confines itself to this story, the relationship between two of the characters is very much reflective on prior events. Additionally, Pleiti has a lot of guilt over events from the first book. On the buy, borrow, toss scale, it is definitely worth a borrow.



Thank you to TOR and NetGalley for the ARC. Clearly, all opinions my own. All quotes subject to change.

[Cait · Rating 3 out of 5]

the idea that nature would save us the trouble of doing away with evil people largely went out of fashion when evil people destroyed nature.

I love to hate / I hate to love / I relate / I cringe / I delight / I scorn

reading malka older is like reading something written by myself, a year ago—by which I do not mean to suggest that I am a better writer than her, no; rather, I have the same experience reading her work that I do reading work written by a past self: it’s both familiar and mortifying.

in particular, older and I share a particular goofy fascination with language, manifested in this series as a sort of...future historical linguistics, exploring the ways in which this particular society under these particular circumstances might speak and coming up with cute new coinages accordingly. and half the time I’m like hell yeah, malka, that was a good one, and then five pages later I’m like oh god, malka, what have you done?

case in point: on ebook loc 67 of 357, a character says, “these accusations weren’t the only attempt to discredit your work, n’esp?” wherein “n’esp?” clearly derives from a truncation of the french “n’est-ce pas?” as in, “[isn’t that] right?” I noted this as a clever little piece of pretension but enjoyed it nonetheless, giving older a little mental fistbump.

then, a scant few pages later, on ebook loc 75, the same character asks, “dafuq?” while “wondering what [she] had missed,” and this brings me immense pain and shame. malka. please. malka!! this should not be allowed. I KNOW YOU THINK YOUR MIXING OF REGISTERS AND HEARKENING BACK TO TO EARLY TWENTY-FIRST CENTURY INTERNET CULTURE IS CUTE AND CLEVER. I DISAGREE EMPHATICALLY AND AM FILLED WITH WRITHING WORMS OF CONTACT EMBARRASSMENT.

I also don’t fully understand why villette is named villette. I feel like I remember something from an earlier book about people’s names in this society intentionally being comprised of random syllables that, combined, were not names in earth languages? but perhaps I’m misremembering.

I can’t put a table in a goodreads review, so here’s a link to ✰✰✰other little language things, aka CAIT’S ETYMOLOGICAL EXPLORATIONS (notttttt an exhaustive list, because undertaking THAT would be exhausting)✰✰✰ (warning however that the list I did compile is still extremely long and tedious lmao)

it does weird me out that for a holmes-and-watson thing this series is so determined to make mossa sober: I peered at her eyes in sudden alarm[...], but no, her pupils seemed normal; if she was altered, it was by her usual addictions: narrative, tea, music. where’s that seven-per-cent solution, babey??

and on the note of mossa, she continues to suck, although I guess she kind of redeems herself a little bit maybe. still: what a shitty girlfriend (sorry, copine). it was actually kind of a relief that she was out of the picture for much of this one. there is, however, one nice, albeit implicit and brief, sex scene.

I like older’s idealistic/utopian ideas about/for city planning re: “the opposing yet complementary urges towards solitude and companionship,” which means that in this world it’s accepted that “residences and workplaces should include both: private space large enough to live or work in, common space that was available but not unavoidable. this was expanded to include various modalities of common space: quiet areas where one might expect not to be unreasonably bothered by the company; convivial spaces where gregariousness was preferred; purposeful spaces, such as game rooms and canteens; less directed spaces open to serendipity and reinterpretation; and everything on the spectrums in between,” all of which allows for the fulfillment of, for example, a desire “to be quietly in company.” sounds ideal to me!

“rationality,” mossa said, “is a tool; and, like any other, it is fallible, and only of use in some circumstances.”

[Brok3n · Rating 4 out of 5]

Pleiti vs the Comemierdas

Novel 3 of Malka Ann Older's Mossa and Pleiti mystery series continues the established scheme of choosing complex abstract noun phrases as titles, in this case The Potency of Ungovernable Impulses.

The Mossa and Pleiti mysteries take place on a future Jupiter (referred to as "Giant"), after humanity has precipitated ecological disasters that left Earth and Mars uninhabitable. The world-building is unusual. In the first two novels Older gave us just barely enough technical information to explain how she imagines humans living on a gas giant plant. I am pretty sure that her scheme would not work, but, hey, at least she came up with something that makes superficial sense.

The physical tech was just outlined, but Older is a sociologist and an advocate for linguistic diversity, and her world-building in those respects is well thought out. The language, in particular, is challenging. I recognize loanwords from Spanish, Japanese, some Germanic language (probably Dutch), and Italian. ("Comemierda" is one such loanword. I won't translate, but Google will help you if you don't recognize it.) There are probably others I didn't recognize. You can generally work out the meaning from context. The linguistic fireworks helped with authenticity, I thought, though I can easily imagine some readers finding it annoying.

The titular characters, Mossa and Pleiti, are described by the publishers as Holmesian, and that description fits better than it usually does. Mossa is an Investigator, that is to say, the closest thing Giant has to a police detective. She's the Holmes of this pair. Pleiti, the Watson, is an academic, and the two are a couple. Mossa is logical, emotionally undemonstrative, and introverted. (In real life those things don't go together, but it is a cliché of fiction to equate logic with unemotionality and social awkwardness.) Pleiti is not a professional Investigator -- her work concerns mining classical fiction for clues about old Earth ecology -- but she gets dragged into Mossa's investigations.

This story is told from Pleiti's point of view, and she starts off the investigation alone. An old friend asks for her help in figuring out who is trying to sabotage the academic career of her (the friend's) cousin, who is a gifted scientist. Pleiti tries to involve Mossa, but Mossa, who is suffering a bout of melancholia, resists, leaving Pleiti to investigate on her own. It's a good story, both the investigation, and Mossa and Pleiti's fraught relationship dynamics, which are presented well enough that even I, a grumpy old aromantic fart, enjoyed them.

I enjoyed the novel as a whole, and will continue to read the series for as long as it stays this good.

Blog review.

[lauraღ · Rating 4 out of 5]

“Rationality is a tool, and like any other, it is fallible, and only of use in some circumstances.”

I had settled on 4 stars, but thinking it over, it's a bit higher? Like, 4.25? IDK, this was just delightful. I've become smitten with Mossa and Pleiti, and this absolutely cemented my love for them. As I said in my review for the second book, this series doesn't quite give me everything I want out of a mystery. But because it's so mentally satisfying in terms of the science fiction, and so emotionally satisfying in terms of the relationship, I feel like I cannot ask for more. Even though I would say that you shouldn't go into this for the romance, the romance is what I love best about it. And it helps to be a lover of classic ACD Holmes, because there were so many little parallels that I could draw between the canon and this retelling, especially in the relationship and the personality quirks of both women.  

But I have to say, right off the bat, that this is definitely a more robust and more involved mystery than the previous books. It helps that it's quite a bit longer, only 50 or so pages from being a full-length novel. And so the author had more time to set up characters, set up plots, delve into little intrigues, introduce us to all of the different players and their motives. I won't say that the mystery was amazing, but unlike in the first two books, there was something tangible for me to chew on and think about and theorise about. I still couldn't figure it out, but I probably could have if I had paid attention to the correct things and thought about certain stuff some more.  In this book, Pleiti has been asked by an old university friend to investigate some threats that her cousin has been getting, threats which seem to be tied to a new invention that she's made that could make breathing easier while outside on the platforms. Pleiti visits her university campus, a different one from her own, and we get to see some of the inter-university rivalry, some of the different platform cultures, language and attitudes. As always, I find the world-building so creative, and I love when we get little nods to history (i.e., our present time).  

This book gave me a little bit of the Baskervilles vibes, because we had, for the first half of the book, Pleiti investigating on her own, trying to protect the client, and also sending updates and missives to Mossa by post. And for other reasons, also. :) There were also some parallels to Homles's depression and malaise, but explored with a bit more depth and nuance. I won't say more, but I came out of this book loving both Mossa and Pleiti so much. Emotionally, this really got me where it counted. There are certain things that I was expecting, and even when it happened exactly as I predicted, there was still such a huge emotional impact. I can think of a lot of Holmesian stories where Holmes's depression is described or alluded to, but it's never quite tackled head-on in a way like this, and I really appreciate Older doing so. Or maybe I just feel like it's being treated profoundly because this relationship is explicitly, exquisitely romantic. Have I mentioned that I adore them? Pleiti is head over heels for Mossa, and has so much love and empathy for her, but she also doesn't let her get away with shit. The relationship is so delightful to me. Even when Pleiti is yearning for Mossa to be there, hoping that she can get her insight and her intellect to help with the case, it never really feels like they're unevenly matched.  And I love that.

We also get a bit of information that impacts on events from the previous, and will def. have ramifications on further books in the series. I'm really excited to see where things go.

Listened to the audiobook as read by Lindsey Dorcus, and, as always, I had a good time with it. This series is just becoming enshrined in my heart. I love them so much.   

“I don’t understand it, Mossa. What is this ungovernable impulse that sends me to you?”
She took a step towards me. “As well ask, Pleiti,” she whispered, “what pushed me to travel partway around the world to be close to you.”

[CarlysGrowingTBR · Rating 4 out of 5]

Academics turn dangerous when Pleiti is asked to investigate some strange attacks against a former peer who's up for a prestigious award.

This is the third installment The Investigations of Mossa and Pleti and it was just as tantalizing and cozy as the previous 2.

Themes:
🪐: Love against all odds
🪐: Women jn STEM

Representation:
💗: Sapphic Lesbian Pairing
💗: Light conversational Spanish
💗: Cuban author/ FMC
💗: Depression Rep

Tropes:
🚀: Love against all odds
🚀: Women in Stem
🚀: Gaspunk Setting

Spice: Closed Door
Triggers: Attempted Murder (non/graphic) see author's website/socials for full list.

Brief Synopsis:
When a former peer starts getting attacked for her controversial research that could create competition for a very well-known and much needed survival item on the planet Giant, Pleiti is contacted by the peers cousin to come in and investigate. Pleiti is unable to rely on Mossa and has to go at it alone, even though it's not her area of expertise. With her own relationship between her and Mossa in turmoil, Pleiti has to start fending off attacks as they start to turn deadly and target Pleiti herself. The can she solve the investigation in time??

General Thoughts:
I really enjoyed this third installment of this series. The cozy mystery was still giving all the vibes that needed to and the setting was still giving gaspunk. It was very interesting to see a different station on the planet, and how it was different from the others we had previously seen. This was the first novel to focus more solely on only one of our dynamic duo. I felt like it worked pretty well. I was more engaged in this mystery than I was in a book two. It felt like it flowed more organically and held my attention better. We continued the storyline between Mossa and Pleiti and their relationship over from the second book into this book and it looks like we're gonna continue it over into a possibly a fourth book? Here's to hoping. I am definitely interested in more novellas in this series.

Disclaimer: I read this as an e-book via Netgalley and TorDotCom. All opinions are my own. This is my honest and voluntary review.

[Rian *fire and books* · Rating 5 out of 5]

This book gave me more anxiety than some thrillers have. I was completely confounded by all the suspects, the weight of Pleiti’s fear and loneliness, and of Mossa’s depression. This was such a heartache to read because it all felt so painfully real.

[Meredith · Rating 4 out of 5]

I love the dynamic between the two main characters and I can’t get enough of the setting!

[Promiscuous Bookworm · Rating 4 out of 5]

Все еще просто хорошо, а не отлично, но мне нравится, как автор в этой серии работает с вкраплениями слов иностранного происхождения, чтобы показать, как со временем трансформировался язык в колонии на Юпитере.

[Chelsea · Rating 4 out of 5]

Thank you to TOR and NetGalley for the ARC.

2025 reading challenge category: A book center LGBTQ+ characters that isn't about coming out

The third installment in the Mossa and Pleiti series and the first longer (though still not LONG) installment. Did it need to be longer? Hm. Well, I don't know what, off the top of my head, I would cut out of it. That said, I don't think it hit any harder than the first two for having extra length.

I always enjoy seeing a new aspect of life on (around?) Giant, and Older does that again, this time going to a rival university of Pleiti's home institution--and partially without Mossa! I definitely did enjoy seeing Pleiti investigate on her own, both instituting what she thought Mossa would do and what felt best to her at any given moment. As always there's an interesting group of supporting characters to add color to the new environment and we even got a slight update as to background developments stemming from one of the previous installments. It DID feel like Older really amped up the language in this one; I'm not talking about the inclusion of Spanish words, but rather the made-up slang and also some just...very academic words, more so even than the academically-minded Pleiti normally used in previous books. I definitely encountered SEVERAL words here that I had to look up if they were real or something Older made up, and I do think we might have crossed the line from "atmospheric" to "slightly off-putting" with some of these choices.

That said, still a VERY enjoyable story as a whole. The "gaslamp investigation on Jupiter" setup is so unique and Older really has built this world so every installment can have its Holmesian core while still having very different settings and supporting casts, which is great. If you're reading this series and enjoying it, you would probably also enjoy A Drop of Corruption which has a similar Holmesian fantasy setup (though without any romance between the main characters).

[Mike · Rating 4 out of 5]

It’s been rainy and unseasonably cold here, so this was the perfect time to return to Giant (better known as Jupiter) and the latest investigation of Mossa & Pleiti. Cozy as always, heartwarming as always, but it was a journey to get there.

The story opens with Mossa’s perspective, debating going to see Pleiti and ultimately deciding not to. Cut to Pleiti; she’s fretting over their relationship, and concerned at the growing distance she perceives between them. Her ruminations are interrupted when an old friend from their university days - Petanj - knocks on her door. Another mutual friend - Villette, Petanj’s cousin - is also in academia, at a university on the far side of Giant, and up for a donship despite her youth. Yet someone is running a smear campaign, accusing Villette of that ultimate academic sin, plagiarism. Villette has heard of Pleiti’s work with Mossa and asks her to come and see who is working against Villette. Pleiti agrees, but makes no promises for Mossa. Which is just as well; Mossa is sunk into a deep depression, and tells Pleiti to leave her alone. So Pleiti goes off to do the investigation on her own.

Malka Older’s academic background shows through clearly. Pleiti finds herself at a distant university with an enormous chip on its collective shoulder about not being Pleiti’s older, prestigious university. She also finds herself, a Classicist, interacting mostly with Modernist scholars, so there’s academic contempt and snobbery and chips on shoulders there as well. But she does her best to find the source of the smear campaign, all the while missing Mossa and feeling like Mossa should be there.

On this, Pleiti and I are of one mind.

Mossa does show up eventually, of course, and emotions between them are fraught. But immediately the book felt more balanced. I’m quite certain this was a deliberate choice on the author’s part; the series needs the dynamic between the two of them.

The actual mystery of this cozy mystery was probably the least satisfying of the three Mossa & Pleiti books published thus far; it felt like mostly noise in the background while Mossa & Pleiti worked things out. The reveal was fine, but didn’t really have much emotional weight for me. Luckily the interpersonal stuff did, which makes this an easy 4 stars.

Comes out on 10 June. Have a cup of coffee/tea/cocoa on standby.

My blog

[Laura · Rating 3 out of 5]

This short novel follows Mossa and Pleiti investigating threats made against a scholar at a university across the planet; when what appears initially to be an attack on the scholar’s research takes a turn toward violence and begins to look more personal, the investigators must try to figure out who is behind it while keeping the scholar safe.

I liked how the mystery was slowly unravelled, and the commentary on academic rivalries and interdepartmental politics felt insightful. I also appreciate Older’s thoughtful depiction of Mossa’s depression. What doesn’t quite work for me in this series is the emphasis on Mossa and Pleiti’s relationship; I am fascinated by the world Older has created, the Classicist vs. Modernist dynamics in the universities, and the varying perspectives on the possibility and timeline of humans potentially returning to Earth. I ultimately wish these were more prominent elements rather than the perpetual miscommunications and pining between the two main characters.

This is the third book in the ‘Investigations of Mossa and Pleiti’ series. While the mystery at the core of the plot is entirely self-contained, I wouldn’t suggest reading this as a standalone as a lot of world-building happens in the earlier books.

Many thanks to Tor and NetGalley for providing me with an ARC to review.

Content warnings: violence, mental health struggle, injury detail

[Lindsay · Rating 2 out of 5]

I was having a hard time with the audiobook and it ended up being re-claimed by the library before I finished, even though I in theory did want to know what was going to happen. The narrator was not to my taste and the story just seemed to be going in circles. Pleiti seemed to be spending a lot of time navel-gazing about Mossa, and the case she was investigating did not grab my attention or interest. And it ended with a surprise (to me) suspect being guilty. This is supposedly loosely based on The Hound of the Baskervilles, which I didn't remember much of. I read a summary of it after I finished this and could see a couple of points mapped on but... meh. This didn't work great for me. I may well read one more if (as seems likely) these keep being written, but I think I would need something more to happen to raise my enthusiasm again.

Also the language thing where she keeps putting random Spanish or Dutch or French or whatever words in to make it sound like the language is evolving-- I found it distracting and not fun. It toook me out of the story.

[Roslyn · Rating 5 out of 5]

This third book in this series felt more fleshed out and real to me, somehow, than the first two, I'd enjoyed them, but I really loved this one. The relationship between Mossa and Pleiti, as difficult as it has been, now feels more real to me as I understand the two infinitely better. I was moved as I watched both of them begin to painfully express their complicated feelings. And there is going to be a change in their lives that promises to be exciting. Looking forward to the next book!

[Miranda · Rating 4 out of 5]

⭐️⭐️⭐️⭐️ The Potency of Ungovernable Impulses is a strong third entry in Malka Older’s Mossa and Pleiti mystery series. I actually enjoyed this one more than the second one, though not as well as the first. As always let’s take the two questions any review of a series needs to cover. Should you start this series at all? This series covers the adventures of two lesbian women who solve mysteries. The catch is that they live on a set of hovering platforms in the middle or upper atmosphere of Jupiter, because climate change has rendered the earth uninhabitable. You’ll have to believe me when I say that these are really cozy mysteries. They have lots of great descriptions of food, and other than the murder it’s got a very calm and small town feel. If you liked Sherlock Holmes, but wish there were more women and also it was in space, it’s worth giving this series a try.

As for this particular entry in the series, it’s a little bit different than the first two. Rather than a cozy mystery, it's got more cozy dark academic thriller vibes. Someone is threatening a researcher at a rival college--a researcher who has just made a very critical breakthrough. There is no shortage of suspects, academic rivals, jilted lovers, industries who stand to lose a lot of money... Pleiti and Mossa will have to stay on their toes to keep this professor safe.

Recommended for fans of Mur Lafferty, The Tainted Cup, and Murder She Wrote.

I received an advance copy in exchange for this honest review.

[Emmaby Barton Grace]

god i am so excited !!

[Shannon Miz · Rating 4 out of 5]

This was my favorite of the series, I think! I enjoyed the plot, but more than that, I felt like the characters were absolutely my favorite! I feel like we really got to know Pleiti so much in this story, and even Mossa (or at least, some of her struggles). That, and the side characters were the most enjoyable in this installment as well, and I do hope we continue to see some of them going forward in the series. I will say, I am so glad I read this on my Kindle! I have a pretty extensive vocabulary, but between Pleiti's next-level vocabulary, and the fact that many of the words in this world are from a variety of languages, it was so much easier to look up on my Kindle (yay technology), so I would think this would be a little more frustrating in a physical or audiobook. Overall, I highly recommend this series, especially this installment, and cannot wait for whatever comes next for Pleiti and Mossa!

[Nicole (bookwyrm) · Rating 3 out of 5]

I think this book suffered from my incredibly high expectations for it. I enjoyed book one, LOVED book two, and I think I was hoping that this third book would follow along on that trend. However, I figured out early in the first half of the book that what I like best about the series is Mossa and Pleiti together. Since they spend the first half of the book apart, with Pleiti mooning over Mossa when she's not working on the case (and even sometimes when she is), I had a very good opportunity to learn what I personally like best about the series. (I've seen other reviews where this alone-time is seen as a good thing for Pleiti's growth; perhaps it is, but it wasn't what I personally was here for.)

The mystery itself was enjoyable, though as with many good Holmesian reimaginings, the reader doesn't have enough of the facts to properly figure out who the culprit is and so my guesses about whodunnit were way off base.

I still enjoyed the setting, characters and world building, and still plan to pick up the next of the books whenever it's written and published. The mish-mash of languages used in the book still worked for me to show that this is not just an English-speaking country evacuated to Jupiter, and it works well to make this a separate culture. I did have to look up more words than normal at first, but later in book I felt that the meaning of the non-English words were more obvious from the context of the rest of the text. All told, I do think this is a good installment to the series, though I'm a little curious / hesitant about the almost (but not quite) 4th-wall-breaking of the very end of the book. Still, I'll happily read more in the series to find out where Older plans to take her characters!

[Rachel (Kalanadi) · Rating 4 out of 5]

3.5 stars

[Pujashree · Rating 4 out of 5]

It is no secret that I ADORE these neurodivergent Jupiter lesbians. Mossa is still inscrutable but depressed, Pleiti is still horny on main for Mossa but sulking about their situationship. So much so that she takes on a case of her own on the other side of the world. This one is a deeply academia-based plot, so your mileage may vary based on how compelling you find those dynamics. Personally, I was having a hard time caring much about the central mystery. My favorite part of revisiting this world is always just seeing more of it and how a post-Earth human society thrives on the edges of a gas giant. More than ever, the most fascinating part of this series for me is the multilingual slangs and how this society studies the history of Earthbound humanity and how to unlearn the limitations of having BEEN Earthbound. The central theme of what constitutes Classical and Modern studies in this world and their relative values is interesting, especially through the lens of an academic. The space detective element, however, is almost non-existent in this one. Thanks Tor and Netgalley for the eARC.

[laurel! · Rating 5 out of 5]

i love this series! it is so much fun and the world is built in such an awesome way!

mossa is certainly sorely missed for the first section of this book --- seeing the way mossa & pleiti interact and work out the mystery between the two of them is one of my favorite parts, and it's sad to see pleiti working on her own!

villette and petanj are great side characters and i hope they continue to appear, although i felt villette was pretty naive at times.

not my favorite of the series (mainly due to the conspicuous absence of my favorite character for part of the book) but definitely worth a read if you liked the rest of the series :D

[rachel x]

i hope this series goes on forever

[Sol]

although i wish i had the kind of familiarity with the original sherlock holmes text enough to appreciate the homage this novella makes, i think even without my prior (and highly encouraged) reacquaintance with them, i'm still able to enjoy this series. this has been true for the first two of this series, and is still true for this third installment. i did enjoy the incredible worldbuilding here, alongside the character and relationship development between the two adorable sapphics. that said im even more inclined now to revisit the classic sherlock novel/s if only to give myself a lil pat in the back when i recognize which specific parts this series paid homage to.

maybe i got teary-eyed towards the end of this one, especially upon reading mossa and pleiti's dialogue. i don't often quote ARCs for the fact that some minor details of certain scenes may still change, but for the hope that this scene will be calcified in my brain, i'll quote this exchange:

"[...] Mossa, truly, if you would listen--when I said I wished I could offer you that trust, what I meant was not that I wished I could trust you, because I do--but that I wish you could trust me enough so that ...so that when you do feel
melancholy, you don't mind my seeing it."
She looked at me at last. "You don't want to see it."
"I don't enjoy seeing you sad, no, but I do want to see you, always." [...]
"But ... it's awful"
"I know, love." [...]
"But why?"
"Mossa. I don't know what impulse pushes you into melancholy. but I promise you, it is no stronger than that which pulls me to you."
A whisper of a smile. "It sounds like an affliction."
"Perhaps, [...] A deep-abiding fever, but a welcome one."
"Pleiti [...] I cannot promise you that I will not again find it impossibly difficult to-to-"
I waited, but she seemed unable
to find a conclusion to the sentence
or perhaps she had found it but
could not admit to it.
"Mossa, you don't have to promise that."
"I wish I could."
"I know."

It's beautiful to find a love like this depicted here. The kind of love that understands deeply, despite not being afflicted by the same woes. The kind of love that wants to see all parts of the other, not just the "easy" ones. The kind of love that says "you don't have to hide; i see all of u and i love you." Oh Mossa and Pleiti.........<3

thank you netgalley and tor books for the e-ARC in exchange for an honest review!

[Sahitya · Rating 5 out of 5]

More of a 4.5 and definitely another favorite of the year.

Mossa and Pleiti series has been a very enjoyable one till now, so I was quite interested in this third installment as well, and turns out this is the best of the three.

The author does a stunning job both plot and character wise in this book. We get a sinister plot trying to discredit and maybe even harm a Modernist scholar, both physically and through her research; and Pleiti taking up the investigation herself in the absence of Mossa. On the other hand, we get a much more detailed look at their dynamic - their feelings for each other, but how they are eclipsed at times by their own insecurities, but still feeling it hard to be away from each other. There were some great conversations between them in the second half of the book, and I always appreciate good communication between a couple, even if doesn’t solve everything instantly. The plot starts off slow, with Pleiti unsure of her sleuthing skills, but her unique scholarly methods of deductions lead to some very explosive and unexpected revelations. It was also very nice to see her get reacquainted with some old college friends, with the possibility that we might meet them again if there are more books in the series(which I sincerely hope there are).

The prose is also so beautiful and hit me particularly at times, with some curious turn of phrase or just the emotion that the author is able to evoke. There is also more world building in this book - we get to see the dynamics in another big university, the rivalries between Unis as well as between the scholars (and how human and earthly it all feels even in a very futuristic setting); and we also get to observe the petty prejudices and discriminations that exist even in this society which supposedly started afresh, after humans had to leave earth. This part of the book made it feel all the more realistic and grounded, despite being set on a gas giant.

Overall, I thoroughly enjoyed the book. The audiobook is also narrated very well and kept me hooked. I have to say that the Holmes and Watson vibes haven’t always been too obvious in this series before, but this book is clearly an ode to The Hound of Baskervilles and considering that it’s one of my all time favorites, I’m not surprised I fell in love with this one too.

[Meg · Rating 5 out of 5]

When a former classmate calls on scholar Pleiti to help with an investigation on a distant platform at another university, Pleiti thinks it may be the thing to help reignite Mossa's interest in her. After what Pleiti thought had been a fairly successful romantic association, Mossa has drifted recently, and Pleiti can't help but wonder if she's at fault.) Mossa grumpily declines, and Pleiti travels to investigate the charges of academic dishonesty against a young scholar up for a prestigious promotion... and ends up in the center of conspiracy, distrust, and longing for Mossa's professional investigatory skills.

I loved this installment of the Mossa and Pleiti series. While the mystery is largely self-contained, you do need to read this series in order to get the best sense of the worldbuilding (and how they can live on Jupiter) and Pleiti's academic background which drives her perspective. Potency gives us honest character development balanced against a mystery high in stakes to those involved.

@yourbookishbff and I both realized an increased use of loanwords from a number of languages that neither of us remember playing as strong a role in the first two books. It feels intentional on Older's part, to start to see a broader cultural background as our POV character Pleiti starts to look outside of her classicist academic shell and sees more perspectives in the world around her.

I love a good novella series, and this sapphic mystery series set on Jupiter hits the spot every time.

Thank you to Tordotcom for an eARC. The Potency of Ungovernable Impulses in out 6/10/25.

[Adam · Rating 4 out of 5]

The Potency of Ungovernable Impulses by Malka Older is the latest instalment in The Investigations of Mossa and Pleiti series, a *inhales* Holmesian sapphic detective series set on an orbital colony above Jupiter. And this, to me, is comfort fiction.

The Mossa and Pleiti stories follow a familiar and effective rhythm - Mossa is the difficult genius investigator, supported by her friend and partner, the empathetic academic Pleiti, as they solve mysteries. The stories are told from Pleiti’s perspective and the sometimes fractious, often tender dynamic between the two leads is both effective and incredibly vindicating for any Johnlock survivors from 2010s Tumblr.

Older pays particular attention to the world she’s created - following humanity rendering Earth uninhabitable, a platform-based society has been developed in space. The world itself is full of loads of interesting choices that could err on cosy (inter-platform trains and dumb waiters for tea) but Older’s presentation of these ideas always fends off accusations of tweeness.

The folly of damaging the Earth is also a prevalent thread throughout the series, exemplified by Pleiti’s academic specialism in researching endemic biospheres detailed in ancient literature, in the hopes of understanding how their people should reseed the earth thoughtfully in the future. It’s a really nice idea thoughtfully explored by Older.

As you may have guessed from all of the above, Mossa & Pleiti can veer a touch esoteric at times but I’m always happy to go along for the ride. One example - Older presents linguistics in the future as having continued to borrow words between languages and the books are rife with lifted terms from Spanish and other languages. With this book, I discovered how to add a Spanish-English dictionary to my ebook app and this helped immeasurably.