The mystery of three quarters

Four people receive letters purporting to be from Hercule Poirot and accusing them each of the murder of Barnabas Pandy, a ninety-something businessman who drowned - accidentally, it seems - in his bath. Poirot has no knowledge of the letters, nor yet of the late Barnabas Pandy, until he is accosted by one of the recipients, society woman Sylvia Rule, before finding another, market trader John McCrodden, in his drawing room. As he begins to investigate the source of the letters with assistance from his young friend Edward Catchpool, a Scotland Yard detective, he comes into contact with the family of Pandy, which seems to be hiding secrets.