A single political entity (the future US) is keeping the world's reins with the threat of time-travel: other countries can either do its bidding, or else. The world has gone horribly wrong, and in this scenario Em and Finn are in jail, kept separated by a solid wall. They can speak, but they can't see each other. They are political rebels, and a mysterious "doctor" wants them to relinquish some important documents. They are being tortured. They can either die there, or escape and use the time-travel machine to go back in time and… well, save the world.That's more or less what the synopsis says.I didn't know what to expect, because I'm no expert on sci-fi; my frame of reference was built upon a brief period of Asimov intoxication in my youth, some Philip Dick here and there, and sporadic episodes of Urania books. So keep that in mind when I tell you that this novel managed to amaze me; if you are a huge reader of sci-fi, maybe you've already seen it all.The most wonderful thing about this book is the surprising clarity of its timeline; from the future, to the past, to bits of future with flashbacks of the past, you're always well aware of where/when you are.If you are prone to philosophical musings about random topics (as I am), you're going to find much food for thought in how time-travel is explained here and how all the paradoxes are dealt with.Another wonderful thing is the tangibility of the character's growth: you begin to know them when they are grown and wiser, and then you get to meet them when they were young. You can see how they got to be the way they are now, and when their older selves meet their younger selves, you can grasp just how much the events changed them.I don't know why this book tried its damnest to keep me away.I saw it sitting on Netgalley's shelves, with its ugly cover, and thought "Oh, what a poor choice of elements to put on a cover, what with all these yellowish outer glows, the dirtied lettering and that silly heart…". Then I saw the blurb from Becca Fitzpatrick and thought "Ugh, just no! No way I'm reading this!"I'm so shallow sometimes.And still I read it, and I'm so glad I did.Note: the hardcover and the kindle edition now have nicer covers.