One night in 1994, Carrie Walsh returns home from a party to find her prostitute mother Sally murdered. Carrie sees a man's shadow on the wall and, whilst phoning the police, observes a man with a bloodstained hand. She is keen to help DI Douglas Hain in his investigation, though the crime ultimately goes unsolved. Fifteen years later, Carrie, now known as Carol, is about to get married. She goes to visit Hain to help put the tragedy of her mother's murder behind her.

Hain explains to Carol his own position fifteen years earlier and how he was dropped from the case because he was a client of Sally's, whom he loved. Hain used Cleo's, the massage parlour where Sally worked, to gain information from her ex-colleagues. He suspects Inspector Oliver of shady dealings with Tony Phillips, the man behind Cleo's. Hain was subsequently given early retirement. Carol herself goes undercover at Cleo's, seeking answers.

In the present day, Carol's obsessive drive to solve her mother's murder finally yields results when she and retired detective Hain discover why Sally was killed and who was responsible. But the journey takes Carol into a world her mum had always concealed, and there is a high price to pay for uncovering the truth about the fateful night in 1994.