At a party in Cornwall hosted by retired actor Sir Charles Cartwright, a local parson named Stephen Babbington suddenly collapses and dies after partaking of a cocktail. Fellow guests include a full cast of 1930s types: a vain and frivolous West End actress, a surly young man of vaguely radical sympathies, a prominent Harley Street specialist, a Bright Young Thing with the bright young name of Egg Lytton Gore—to list only a few of them. Also on hand is Hercule Poirot. After Babbington’s death, Sir Charles raises the idea of foul play, but Poirot dismisses it. Who, the little Belgian asks, would want to slay a harmless country clergyman? But, after another man dies in a similar fashion at a similar party with a very similar guest list, the great detective joins the great thespian in surmising that a diabolical killer has been at work.
The mystery that Poirot eventually unravels falls in the lower tier of the conundrums that Christie set for him during the 1930s, the heyday of her (and his) puzzle-plot mastery. She applies less skill and effort than usual to the job of distributing suspicion across a wide range of potential murderers, and she neglects to fit a few loose pieces of the puzzle into her solution. In compensation, though, she deftly uses the metaphor of the stage to explore the stagecraft at the heart of the detective story. She also gives extra attention to the consideration, and the concealment, of homicidal motive—a major strength of hers throughout her long and devious career.
(A curious sidelight: Christie makes narrative use of a sanitarium in Yorkshire for victims of nervous exhaustion. It was to just such a place that Christie herself absconded during her famous disappearance in 1926, a disappearance that she otherwise refused to discuss publicly for the rest of her life.)