The pauper's body, washed, shaved and manicured, was then carried over the roofs and dumped in Thipps' bath as a joke. He dismembered Sir Reuben and gave him to his students to dissect, substituting his body for that of a pauper donated to the hospital for that purpose, who bore a superficial resemblance to Sir Reuben.

He also engineered the trading in mining shares, to lure Sir Reuben to his death. Wimsey finally unravels the gruesome truth: Freke murdered Sir Reuben and staged his 'disappearance' from home, having borne a grudge for years over Lady Levy, who chose to marry Sir Reuben rather than him. The trail leads to the prestigious teaching hospital next door to the architect's flat, and to the eminent surgeon and neurologist Sir Julian Freke who is based there.

The corpse in the bath is not Levy, but as matters unfold Wimsey becomes convinced that the two are linked. Inspector Parker, Wimsey's friend, is investigating this. Meanwhile, Sir Reuben Levy, a famous financier, has apparently disappeared into thin air in his own bedroom, and there has been an odd little flurry of trading in some mining shares, long believed defunct. Ignoring the clumsy efforts of the official investigator, Inspector Sugg, who suspects Thipps and his servant, Wimsey starts his own enquiry. From Wikipedia: Wimsey's mother, the Dowager Duchess of Denver, telephones to say that Thipps, the architect her vicar has hired to do some work on the church, has just found a dead body in the bath in the flat where he lives: a body wearing nothing but a pair of pince-nez.

Whose Body? by Dorothy L. Sayers