When the body of a young man is discovered in a derelict building, DCI Cassie Stuart (Nicola Walker) – one of the Met's smartest detectives – is called in to investigate with her partner, DI Sunil Khan (Sanjeev Bhaskar). Jimmy Sullivan was a homeless boy, murdered in 1976 when the building was a hostel. His diary implicates four suspects; a clergyman, an eminent entrepreneur, a community worker and a wheelchair-bound husband caring for his wife. Each has a secret to hide. As their lies unravel, the people they love most begin to wonder what else they might be capable of. Nothing in this case is black and white. Can you ever really know the people closest to you? What secrets have they buried?