All Our Yesterdays, by Cristin Terrill (Disney-Hyperion, September 2013, YA) is a very good book that is best read without any spoilers. I considered just using the fairly spoiler-free publishers blurb, and adding to it, but I don't think it captures the story all that well. So. You can go read the book now, if you want to.
How far would you go to make sure that the present you are living in would never happen? What would happen if you used a time machine to fix mistakes in the past...and the power that you felt swept you onward, until you changed so much that those who once loved you no longer could? Would you kill someone, if you knew that doing so would save your future self (and other people)?
Em and Finn have tried 14 different ways to make sure the present they are living (tortured and imprisoned in a brutal police state) won't happen. 14 times they have gone back 4 years into the past...and each time the changes they made weren't enough to keep them from ending up in the same old prison cell, reading the notes hidden in the cell drain from their past attempts. And now they are going back again, this time knowing that killing the inventor of the time machine is the only thing they haven't tried.
But of course, four years back in the past, there are their young selves, still trusting and all unaware. There is also James, brilliant, damaged, and best friend to each of them, and maybe more to young Em--he is the sun around which she revolves. And there is the person who will become their enemy, snarled inexorably into the fabric of their lives....
In a series of alternating narrations, from the points of view of Finn and Em in the present, and the time-travelling Finn and Em, the reader learns how all the snarling came to be. And in the process, all four characters, and James, become real and human and hurt...and on top of that, there are personal and political machinations, and tension-filled reveals, dolled out with heavy inevitability, about what happened in the four gap years that led to the point of no return. Gripping as all get out.
My only substantive complaint is that I wish it had been made clearer when the arrival of the time travelers began to change things. I didn't pick up on when that had started, and so I was confused for 25 or so pages. My only complaint with the story is that Finn and Em have to assume that the choice they are making is better than the alternative...and certainly it is to them, and who knows what other evils the time machine and its master would be capable of. But they also know, having watched time ebb and flow as things were "fixed," that some of the things that might happen without the time machine are pretty darn awful. They don't allow themselves to think to much about that, and I guess it's good to have ambiguity and tension, and no happy ever after, but I wasn't sure this was an Addition, as opposed to a distraction. (This is a long paragraph, and I thought about editing it, but am leaving it in as an example of how the book thought-provoked me).
Just to say--as well as all the exiting and complex and beautifully tricksy time travelling, there is also a very nice and cheer-worthy romance, which lightened the mood in a much needed way.
I can imagine wanting to re-read it at some point, which is pretty high praise given how many un-read books I have kicking around.
Final thought: Cristin Terrill has psychically seen the inside of my house, and uses it the model for Finn's: "None of the furniture matches, and practically every surface has something on it that shouldn't be there: a stack of old newspapers, a half-full coffee cup, a discarded sweater. There's a pile of dishes in a sink and a stack of folded laundry on the sofa, like someone hit the pause button on life." Except of course that instead of stacks of newspapers, there are stacks of books. (I do try to tidy up before company comes, but there's not much one can do about the furniture. Or the books).