In spite of Chief Superintendent Innocent's orders to the contrary, DI Lewis continues to investigate the supposed suicide of housewife Rachel Mallory. Regardless of the replacement coroner's findings, Lewis simply cannot find a single reason why the attractive woman would take her own life. She was married to a successful optometrist, Hugh Mallory, had two lovely children and a good circle of friends. As Lewis and Hathaway dig deeper into the case they obtain two important pieces of information. The first is that Hugh and Rachel weren't married but actually part of a wife swap that occurred some years before with Hugh's business partner. The second comes from a eccentric Oxford professor who promises the police an important piece of information in return for a favor.