The Cretan Bull

Hercule Poirot is asked for assistance by a young lady, Diana Maberly. She was engaged to marry Hugh Chandler for over a year but he has broken it off as he thinks he is going mad. There is a history of insanity in the family, with his grandfather and a great aunt being afflicted, and his father, Admiral Chandler, has insisted his son leave the Navy before his condition worsens, but the reason was hidden under the pretext of having to manage the family country estate – a reason no one believed, including Colonel Frobisher, a family friend and Hugh's godfather. At Poirot's prompting, Diana admits that there have been some unusual occurrences on nearby farms with the throats of sheep cut and the like but insists it has nothing to do with the situation. The Admiral refuses to let a doctor see his son.

Poirot travels with Diana to the family seat of Lyde Manor where he meets the people involved. Hugh strikes Poirot as a fine young bull of a man. He learns further details of the history of insanity in the family from Colonel Frobisher, including Hugh's grandfather who was committed to an asylum. Poirot learns that Hugh's mother died when he was ten years old in a boating accident when she was out with the Admiral, and that she was previously engaged to Frobisher before he went off to India with the British Army. When he came home, he learned she had married Admiral Chandler; however, this incident did nothing to lessen the ties of friendship between the two men.

Poirot forces Frobisher to tell him more details of the incident with the sheep and finds out that on the night concerned, the Admiral found his son in bed with blood on his clothes and blood in the washbasin but Hugh remembered nothing of what he had done. Poirot questions the Admiral who has aged immensely since these incidents started and who feels that breaking the engagement is best for everyone, remarking that there will be no more Chandlers at Lyde Manor after he and his son have died.

In questioning Hugh, Poirot hears of his dreams which always seem to include elements of hydrophobia. He also suffers from hallucinations and has one while speaking to Poirot of seeing a skeletal figure in the garden. Poirot, however, is convinced that Hugh is sane and begins his investigations, asking Diana to arrange for him to spend the night in the manor. He searches Hugh's room and also makes a trip to a local chemist, supposedly to buy a toothbrush.

That night, Hugh somehow manages to get out of his locked room and is found outside Diana's room, a bloodied knife in his hands from having killed a cat. Hugh recovers consciousness, is shocked to hear what has happened and tells the others that he intends to go out shooting rabbits. It is clear that his real intention is to commit suicide in the woods with a shotgun and therefore save himself and the others from further pain. Poirot stops him and tells them all that Hugh is being set up to kill himself.

The culprit decided to use the Admiral's atropine eyedrops to induce madness in Hugh, inspired by Frobisher's accounts of datura poisoning in India. The atropine was mixed into Hugh's shaving cream so that it could be absorbed through his skin, causing hallucinations and intense thirst, and the culprit killed the animals and planted evidence to frame him. Poirot accuses the Admiral of being responsible; he had discovered that Hugh was actually Frobisher's son, caused the drowning to punish Mrs Chandler for her infidelity, and conceived the plot to eliminate Hugh. The Admiral, suffering from the family's hereditary madness, had prevented Hugh from seeing a doctor because an examination would have confirmed his sanity. Poirot had verified his theory by having the chemist test a sample of Hugh's shaving cream and noting his and Frobisher's similar mannerisms.

The Admiral scoffs at Poirot's explanation, then takes Hugh's shotgun and goes into the woods to hunt rabbits. A shot is heard shortly after.