The Jane Doe series is a complicated and nuanced read, and it'd been a while since I read book 1 (read my review from 2019 here) so I had a bit of a time to get into it again. But once I did, it was a great read.
It starts with a prologue from the villain, in Roth's POV, which is the only time we get this, but in it he learns Jane has no idea she's the third key to the Cradle, which Roth wants to use to release the Cradle Sea and wipe out the Manor and any worlds attached to it.
Jane has escaped the Maze, the labyrinth of the Manor, but the worlds it connects are still slowly dying, disappearing (Earth included) and shrinking ever-faster. Winnifred the Earth librarian waits for the right time to lead what remains of Earth's people to fight Roth and save Jane.
Jane finds herself on a desert planet, separated from her friends after she storms off and a sandstorm blows in. She's found her "mom," Elsa, her father John's wife, and the woman is not at all what she imagined. Least of all motherly.
It turns out Winifred the librarian back on Earth is a bit of a legendary figure in this world, for having fought Roth successfully once, a millennia ago. But she hasn't been seen in a long, long time, and Jane's mom, Elsa, is not exactly glad to see her "daughter" back.
Because Jane isn't Elsa's daughter, and Roth killed her little boy, her son, and in some ways she blames Jane and John for that.
Jane thinks she relatively safe on Roth's home world, as it's the last place he'll look for her. She must stay free from opposing factions, both of whom want her for their own purposes, while learning as much about Roth as she can -- where he came from, what he was like before he turned evil, before he was entombed below a palace but doomed to live forever while rotting away at the same time, creating the horrible creature he is now. She must find his one weakness -- the arrowhead that can kill him.
Except someone's already found it, and now that they've got Jane, they plan on serving her up on a silver platter to Roth. With help from enemies turned allies (including a Leatherback!), she'll make it to the Cradle Sea before Roth, with her trusted friend (and crush) Violet and Roth's mercenary, Hickory.
I won't spoil what happens, just know it's a wonderful twist and a fantastic fantasy read!