The Girdle of Hyppolita

Alexander Simpson asks Hercule Poirot to help in the investigation of a painting by Rubens which was stolen from the gallery that he owns. A group of unemployed men were paid to carry out a demonstration in the gallery which, once it was cleared by the police, was found to have been a diversion to enable the picture to be cut out of its frame. Simpson knows the picture is being transported to France where it will be bought by a millionaire collector and he wants Poirot to assist as he thinks he will be better at dealing with an unscrupulous rich man than the police will be.

Poirot reluctantly agrees to help. He is far more interested in a case that Japp has about Winnie King, a fifteen-year-old English girl who was being escorted to Paris as one of a party of such girls for the new term at Miss Pope's exclusive school there. On the way back from the dining car of the train, just after it left Amiens (the last stop before Paris), Winnie King went into the toilet and seemingly vanished. No body has been found by the side of the tracks and the train made no other stops, only slowing down for a signal. However, Winnie's hat was later recovered near the tracks. Poirot asks if her shoes have been found.

Some time later, Japp phones Poirot and tells him Winnie has been found about 15 mi (24 km) from Amiens. She is in a daze, has been doped according to the doctor who examined her, and is unable to remember much after setting off from her home town of Cranchester. She remembers nothing of meeting one of Miss Pope's staff, Miss Burshaw, in London before the trip to France. Despite the girl being found, Poirot speaks with Detective Inspector Hearn, who has been dealing with the case and is no nearer to solving the mystery of how the girl disappeared. The only other people in the carriage seemed clear of suspicion – two middle-aged spinsters, two French commercial travellers from Lyon, a young man called James Elliot and his flashy wife, and an American lady about whom very little is known. He is able to confirm that Winnie's shoes were found by the rail line which confirms Poirot's theory.

Poirot goes to France and visits Miss Pope's establishment at Neuilly. The formidable headmistress tells Poirot of the advantages of her school being close to the music and culture of Paris. He hears how two sets of Parisian police asked to search through Winnie's trunk, neither seemingly having spoken to the other, and sees a badly painted picture in oils depicting the bridge at Cranchester, executed by Winnie as a present for Miss Pope. In front of the startled woman, Poirot begins to scrub the picture with turpentine whilst telling her that Winnie never made the trip across to France.

Miss Burshaw met a girl in London whom she had never seen before, and who then totally changed her appearance in the toilette on the train, discarding the schoolgirl hat and shoes through the window and transforming herself into the flashy wife of James Elliot. At the same time, Poirot has stripped away Winnie's "dreadful" painting to expose a second one beneath it: the Girdle of Hippolyta, the missing Rubens masterpiece.

The thieves smuggled the painting in an escorted schoolgirl's trunk, knowing such a thing would never be searched by customs, and one of the gang then threw off her disguise of a plain schoolgirl. Other members of the gang, disguised as policemen, could search the trunk later and retrieve the painting. They did not know that Miss Pope, who insisted on trunks being unpacked upon arrival, would find the "present" and take possession of it immediately. When Poirot leaves, the girls swarm around him asking for his autograph which Poirot refers to as the attack by the Amazons.