Part one, Sleepyhead, follows Thorne, who, while investigating a series of attacks on young women, is dragged back into the nightmares of his past as he races to find a killer.

Part two, Scaredycat, sees two women murdered within hours of one another near St Pancras station, but in different ways. When a connection is made with two other murders which occurred months before, but also on the same day, Thorne realises two serial killers may be in a macabre partnership.