After a horrific bus crash that killed twenty-one of their classmates, the two survivors are lying on hospital beds, comatose and with only a slim chance of recovery. But when Toby and Lyssie wake up, everything has changed. Everyone has disappeared, they don't know where they are, and there's a huge crack in the sky that isn't going away. Trying to piece together what's happened, they have to try to understand and survive in an unfamiliar world that doesn't make sense.