Learned Chief Inspector Barnaby and callow Sergeant Troy go to work when importunate, elderly Miss Bellringer insists that her friend, Emily Simpson, did not die of a heart attack as her doctor claimed, but was murdered. An autopsy proves Miss Bellringer right; Emily had imbibed a Socratic mix of wine and hemlock. Spreading alarm throughout the community, an unseen murderer strikes again, leaving sly Mrs. Rainbird's bloody corpse to be found by her son, the local undertaker. As Barnaby and Troy investigate, they turn up evidence of another crime years earlier, and several suspects. Among them are the doctor's promiscuous wife, a young woman whose brother objects to her marriage to a rich widower and a Lady Chatterley-type gamekeeper. Diligent detecting brings the chief and his bumbling assistant to a sensational expose.