What's the Name of That Book??? discussion

it was a middle grade book read in the past 5 years with a bright green cover with the title in yellow capitals. The word lost I think. The plot was the whole time you're made to think the MC is stranded after some incident in some terrible place - there's a ravine and he lives underground? with other people? and he doesn't know where he is. slowly at the end he figured things out, he is near his neighbourhood but has somehow turned tiny, the ravine is actually just a small ditch or something. at the end of the book he returns home, there's his sister called emma (normal sized), after he grows normal sized he returns to the ravine place but now can't find/see the tiny people he lived with
I remember thinking that it was a very bad book but now I want to find it

Maybe something in the Andrew Lost series?

https://www.goodreads.com/series/6802...

Andrew Lost On the Dog is the first book.

nope, unfortunately
i vividly remember just a solid green cover and I think maybe a black silhouette? and the title in block yellow capitals. the back cover featured small covers in the rest of the series i assume? all different solid colours with short words in bold letters (like lost). i feel like there was smaller writing below that which was the rest of the title but im not sure. i owned this a couple years ago as a paperback but then gave it away

update: i found it after an extensive (and infuriating lol) prompt with chatgpt.
The Dark Ground by Gillian Cross

Good news, glad you found it!