This was quite possibly my favorite read of the year. It’s definitely up there among the top ten.
Five stars, no question. This has cool time travel with science behind it that didn’t contradict itself. We get some interesting ideas of how time travel might work, how it would relate to the theory of relativity, and a great hypothesis about time having a sentient aspect to it. Our characters are varied and deep. Their relationships to each other are interesting.
We also get to see the future and past versions of some of the characters. I can’t get over how fascinating it was to see the similarities and differences between them. They’re four years apart, but they’ve changed so much. It makes me wonder how much I’ve changed in recent years.
Anyways, before we go further, let’s look at the blurb:
What would you change?
Imprisoned in the heart of a secret military base, Em has nothing except the voice of the boy in the cell next door and the list of instructions she finds taped inside the drain.
Only Em can complete the final instruction. She’s tried everything to prevent the creation of a time machine that will tear the world apart. She holds the proof: a list she has never seen before, written in her own hand. Each failed attempt in the past has led her to the same terrible present—imprisoned and tortured by a sadistic man called the doctor while war rages outside.
Marina has loved her best friend, James, since they were children. A gorgeous, introverted science prodigy from one of America’s most famous families, James finally seems to be seeing Marina in a new way, too. But on one disastrous night, James’s life crumbles, and with it, Marina’s hopes for their future. Marina will protect James, no matter what. Even if it means opening her eyes to a truth so terrible that she may not survive it… at least, not as the girl she once was. Em and Marina are in a race against time that only one of them can win.
All Our Yesterdays is a wrenching, brilliantly plotted story of fierce love, unthinkable sacrifice, and the infinite implications of our every choice.
Cool idea, check. Deep, complex, and consistent characters, check. Brilliant plot, check. Heart-wrenching everything, check. Believable world, check. Plus there are a lot of themes running through this book about morality. Should you kill the few to save the many? What does it take for a person to be considered evil? Because that’s the thing. There are no evil characters in this book. People do things that can be considered evil, but everyone thinks they’re doing the ‘right thing.’
This is one of those brilliant books that shows very clearly that everyone is a hero. Even the villains are heroes in their own minds. It’s all left quite open as well, so we’re not told that our guy’s side is the right one. They believe it’s the right one, but I imagine if we were on the other side their conviction would be just as strong. This book left me with a lot of thoughts, and tons of feelings.
The words kept me gripped from start to finish, so go read it. I hope you enjoy it as much as I did.
For more reviews on this book go to: https://www.goodreads.com/book/show/13514612-all-our-yesterdays
samaustinwriter 
I listened to this one on audio book last year. It’s amazing. Great review!