'The Affair at the Mystery Ball', tx. 3/3/1991

Eustace Beltrane and his nephew Lord Cronshaw argue about money, as Eustace wants to buy an expensive china tea set. On their way to the Victory Ball, they are joined by radio actors Coco Courtney and Chris Davidson, Davidson's wife and Eustace's friend Mrs Mallaby. All are masked and dressed as characters from Italian Commedia dell'Arte. Hastings and Poirot arrive at the ball at the invitation of BBC producer James Ackerley, who is hoping to convince the detective to relate some of his cases on radio.

Coco and Cronshaw row and Chris takes Coco home. Shortly before midnight, Madame Mallaby spots Cronshaw on a balcony, writing in his notebook. They wave to each other and she goes upstairs to join him. There she finds Cronshaw's dead body. He has been stabbed. In his pocket Hastings finds a handkerchief containing cocaine. Japp also finds a notebook with the word 'Lowestoft' written in it. Poirot cryptically remarks that the curtained recess behind the body is of special significance.

The following morning, Poirot reads in Cronshaw's obituary that he supported the 'League Against Drug Addiction'. Japp discovers the body of Coco in her flat, dead from an overdose of cocaine. Poirot explains that Cronshaw had been trying to stop her addiction and that this was why they quarrelled.

At the morgue, Poirot finds in Cronshaw's clenched fist a pom pom from one of the Davidson's Ball costumes. Poirot and Hastings go to see Mrs Davidson and find that her costume has a pom pom missing. As they leave, Poirot tells Japp that the 'Lowestoft' scribbled in the notebook probably referred to a kind of china, indicating Eustace as a suspect.

Poirot reunites all the suspects at the BBC for a live broadcast. He reveals that Chris had been Coco's drug supplier and that he killed Cronshaw to avoid exposure. He then hid the body in the recess and took Coco home, giving her a lethal dose of cocaine. He then returned to the Ball dressed as Cronshaw, where he was seen by Mrs Mallaby, thereby giving himself an alibi by suggesting the murder occurred much later than it really did. He scribbled in the notebook to cast suspicion on Eustace, and cut the pom pom from his wife's costume to incriminate her. The final proof is that he wrote in the notebook with his left hand, while Cronshaw was right-handed.