London detectives investigate crimes from the past, unravelling secrets left buried for years.

When the body of a young man is discovered in a derelict building, Detective Chief Inspector (DCI) Cassie Stuart is called in to investigate with her partner, Detective Sergeant (DS) Sunil "Sunny" Khan (Sanjeev Bhaskar). Jimmy Sullivan was a homeless runaway, murdered in 1976 when the building was a hostel. His diary implicates four suspects: a clergyman, an eminent entrepreneur, a community worker, and a disabled house-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?