How much of a monster do you have to become to hunt monsters? Detective John Cain is a hard man. He's been working homicides long enough that he can withstand almost anything, even wrenching personal loss. But everyone has a limit, as he discovers when assigned to the investigation of a child killing. It's not enough to be a good cop, to follow the procedure and ensure that scum go to prison. To honor the chilling promise he gave to the dead child's parents -- to find the killer using any means necessary -- Cain will have to cross lines and do whatever it takes to bring bloody justice to the killer.