How do you catch a killer who is yet to kill? We've all heard about the signs: coldness, cruelty, lack of empathy. DI Tom Thorne knows the psychological profile of a psychopath all too well, so when pets start disappearing on suburban London streets, he sees a chance to stop a future murderer. The journey brings him face to face with a killer who will tear lives apart. Inspired by a dramatic real-life case.