Stopping in at the Piccadilly Palace Hotel for a bit of afternoon refreshment, Mr. Ambrose Chitterwick witnesses a chilling scene: an elderly lady dies of poisoning in the midst of a crowded lounge. An empty vial in her hand and a residue of prussic acid in her coffee cup suggest the means of death; but was it suicide or murder?

Scotland Yard contends she was poisoned by Major Sinclair, her nephew and putative heir who had been sitting with her at her table. Moreover, Inspector Moresby of Scotland Yard has tapped Chitterwick as chief witness for the prosecution. But after a chorus of friends and relatives claim the accused is incapable of such a crime, Chitterwick's interest -and involvement - in the case deepen. Mystery lovers will need their ratiocinative skills in top working order to keep up with the twists and turns of the plot as the timorous sleuth (he recites "The Wreck of the Hesperus" to calm himself in tense situations) threads his way through a thicket of contradictory clues.