Aboard the Prometheus, an afternoon passenger flight from Paris to Croydon, eleven travellers settle in for the short crossing to England. Among them sits Hercule Poirot, idly observing his fellow passengers: a young hairdresser, a quiet dentist, two French archaeologists, a mystery novelist, a doctor, a businessman, and an unhappy society countess. At the rear of the cabin, a wealthy French moneylender named Madame Giselle dozes alone. When the aeroplane begins its descent, she is found dead in her seat, a small puncture on her neck. At first a wasp sting seems the obvious explanation, but Poirot notices a tiny poisoned thorn on the floor and a blowpipe concealed nearby. The killer, it becomes clear, was confined to the cabin throughout the flight, which makes every passenger a suspect and Poirot himself one of the accused. Working alongside Inspector Japp, Poirot must untangle the tangled affairs of a victim who lent money on the strength of other people's secrets. As he sifts the alibis, motives, and half-truths of a closed circle of strangers, the question is not how the impossible weapon was used in plain sight, but which of these ordinary travellers had reason enough to kill. The result is a tightly constructed puzzle that rewards careful attention to detail.