The Affair at the Victory Ball by Agatha Christie, a Poirot short story published 7 March 1923 – Issue 1571 (This was Christie's first published short story).
.Chief Inspector Japp asks Poirot to assist Scotland Yard in the strange events which took place at a recent costumed Victory Ball. A group of six people, headed by the young Viscount Cronshaw, attended dressed in the costume of the Commedia dell'arte. Lord Cronshaw was Harlequin, his uncle, the honourable Eustace Beltane, was Punchinello and Mrs Mallaby, an American widow, was Punchinella. In the roles of Pierrot and Pierrette were Mr and Mrs Christopher Davidson (he being a stage actor) and finally, Miss "Coco" Courtenay, an actress rumoured to be engaged to Lord Cronshaw, was Columbine. The night went badly from the start when it was obvious to the party that Cronshaw and Miss Courtenay were not on speaking terms. The latter was crying and asked Chris Davidson to take her home to her flat in Chelsea. When they had gone, a friend of Cronshaw's spotted Harlequin in a box looking down on the ball and called up to him to join them on the main floor. Cronshaw left the box to join them but then disappeared. He was found ten minutes later on the floor of the supper room, stabbed through the heart with a table knife, his body strangely stiff.