Orphan Alice Valentine becomes the first sixteen-year-old at her local university. Then her whole world changes the night a werewolf attacks her. But even that isn’t as strange as discovering she has an identical twin sister, Cassie. And Cassie kills werewolves. And all the other monsters Alice didn’t believe existed.

Alice and Cassie set off to discover what happened to their parents, a journey that takes them from northern England to the edge of the apocalypse, unsure if they will save the world or destroy it.