"You have to kill him." 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 apart, 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.