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.

Others are less convinced, so Thorne relies on DI Nicola Tanner to help him solve the case, before the culprit starts hunting people. The journey brings them face to face with a killer who will tear their lives apart.