Thipps, an architect, finds a dead body wearing nothing but a pair of pince-nez in the bath of his London flat. Lord Peter Wimsey-a nobleman who has recently developed an interest in criminal investigation as a hobby-resolves to investigate the matter privately. Leading the official investigation is Inspector Sugg, who suggests that the body may be that of the famous financier Sir Reuben Levy, who disappeared from his bedroom in mysterious circumstances the night before. Sir Reuben's disappearance is in the hands of Inspector Charles Parker, a friend of Wimsey's. Although the body in the bath superficially resembles that of Sir Reuben, it quickly becomes clear that it is not him, and it appears that the cases may be unconnected. Wimsey joins Parker in his investigation.Thipps's flat is near a teaching hospital, and Wimsey considers the possibility that the unexpected appearance of a body may have been the result of a joke perpetrated by one of the medical students. However, that is excluded by evidence given at the inquest by the respected surgeon and neurologist Sir Julian Freke, who states that there was no subject missing from his dissecting room.A prostitute's chance encounter with Levy on the night of his disappearance, on the road leading to the hospital and to Sir Julian Freke's house next door, provides Wimsey with the clue that allows him to link the two cases. Freke maintains that he was discreetly being consulted by Levy about a medical problem, and that Levy left at about 10pm. Freke's manservant reports that Freke was inexplicably taking a bath at about 3 o'clock the following morning, judging from the noise of the cistern.Wimsey ultimately discovers that Freke murdered Sir Reuben after luring him to his house with the promise of some inside financial information. Freke smuggled the body out onto the roof under cover of the cistern noise, took it into the hospital, and substituted it for that of a pauper who had been donated for dissection by the local workhouse. He then visited Sir Reuben's home to stage his disappearance, returned, carried the pauper's body over the flat roofs of the nearby houses and placed it in Thipps' bath, entering via a bathroom window that had been left open. As a joke, he added a pair of pince-nez that had by chance come into his possession. Returning to the hospital, he prepared Sir Reuben's body for dissection, giving it to his medical students for that purpose the next day.Freke unsuccessfully attempts to murder both Parker and Wimsey. When it becomes clear that his actions have been discovered, he prepares a written confession of his long-held desire for revenge: many years earlier, he hoped to marry the woman who later became Lady Levy, but she chose Sir Reuben in preference to him. He also intended to substantiate his own theory of mind, in which conscience, a sense of responsibility and so on are merely "surface symptoms" which arise from physical irritation or damage to the tissues of the brain. As he completes the confession the police arrive to arrest him, preventing his suicide just in time.