When Poirot's dentist turned up shot in the head less within hours of treating the Belgian detective, Poirot was not satisfied with the apparent lack of motive, and got even more curious when the motive was helpfully provided later in the form of another patient of the dentist dying of malpractice.
Amidst the array of witnesses; those who had been present on the scene at some time or other on the same day, Poirot tried to piece together a puzzling picture; who was, or is, the intended victim ? How were the persons of Blunt, a most influential figure in the world of British finance who remained largely in the background ? Or the rebellious Raikes who was in love with the niece of Blunt ? Or the retired civil servant Barnes ? Or the mysterious missionary lady Seale who inexplicable went missing soon after?
Red herrings abound in this story, with numerous twists and turns. The time interval was long, with weeks or more passing between chapters, making one marvel at how Poirot managed to keep the right focus on the murder even though he must have attended to numerous other affairs in the meantime.
Unhappily, when all was revealed, what the book lacked was a credible motive for the murder of the dentist. Given the resources available to and the intellect of the culprit, the killing seemed most unnecessary.