Double Sin

Whilst holidaying in Ebermouth, on the south Devon coast, with Hastings, Hercule Poirot receives a letter from a friend asking to meet him at Charlock Bay, on the north Devon coast. To Poirot's initial chagrin, Hastings wishes to travel by motor coach rather than train. However, at the booking office, Poirot is intrigued by two other passengers — a young woman, whom Hastings admires, and a young man with a poorly grown moustache.

During the journey, the young woman introduces herself as Mary Durrant. She is travelling to Charlock Bay on behalf of her aunt, Elizabeth Penn, to deliver a valuable set of miniatures to an American collector there by the name of J. Baker Wood.

When the coach stops in Monkhampton, Poirot, Hastings, and Miss Durrant take lunch together at a hotel. But Ms Durrant, who is facing the window, leaves abruptly. Upon returning, she apologises, saying that she mistakenly thought a man was removing her suitcase, containing the miniatures, from the coach. The man she describes is the young man with the poorly grown moustache, Norton Kane.

Later, in Charlock Bay, Miss Durrant informs Poirot and Hastings that a crocodile despatch case which was inside the suitcase, and which contained the miniatures, is empty and that the lock has been forced. Poirot wonders why a thief would force the lock and remove the miniatures rather than simply take the whole despatch case and open it at their leisure. Poirot telephones Mr Wood, who says that he bought the miniatures just half an hour earlier from a representative of Elizabeth Penn. Poirot and Hastings visit Mr Wood, who describes the representative as a tall, middle-aged woman with grey hair, a blotchy complexion, and a budding moustache.

Returning to Ebermouth, Poirot and Hastings visit Miss Penn's shop and find her to be an elderly lady. Poirot concludes that the theft was staged by Miss Durrant and Miss Penn. Miss Durrant had lied about Kane tampering with the suitcase, to cast suspicion on him. Meanwhile, Miss Penn, disguised as a younger woman, visited Mr Wood and sold him the miniatures. Mr Wood, however, would ultimately have had to return the miniatures, because they were officially stolen goods. Miss Durrant and Miss Penn would have kept the five hundred pounds and still possessed the miniatures.