Time travel works like this:

Everyone has a chronal signature. It's built into your very cells, and it's what keeps time travelers from being seen. Go forward, go back, it doesn't matter. You can't interact with another time because you're not from that time. On the one hand, it makes returning extremely easy, as your chronal signature works like a tether. On the other, it means that time travel is now the domain of bored tourists and stuffy historians.

But not Danni Xhang. She's figured it out,