In London, a tense public dressing-down of scandalous literature sparks a tangled, farcical mystery. Archibald Soper, Louis Jouvet the Bishop of Bedford, denounces Felix Chapel’s latest crime novel at a sparsely attended meeting. Among the attendees is his cousin Irwin Molyneux, Michel Simon, who is invited to speak but is abruptly interrupted by William Kramps, Jean-Louis Barrault, a ruthless serial killer on the loose. The uproar that follows drives Soper to an impulsive, later-night decision: he invites himself to dine and sleep at the Molyneux house, dragging a wave of social oddities into a house already unsettled by the disappearance of Mrs. Molyneux.
That evening, Mrs. Molyneux’s household is in turmoil. Her servants have just left, and she, pretending to be called away, cooks the meal while Eva, the Molyneux secretary, Nadine Vogel serves. Soper fixes on the oddity of Molyneux’s excuses for his wife’s absence, and as night settles in, the couple slips away to a boarding house in Chinatown, unaware that William Kramps has taken a room in the very next unit. By morning, with both spouses gone, Soper rings Scotland Yard, and London becomes absorbed in a city-wide whodunit.
The press, eager for a hook, hires Felix Chapel to probe the mystery. The twist is that Felix Chapel is really Irwin Molyneux in a false beard, though he’s wholly inept at crafting a real mystery because his plots come from Eva, who confesses their inspiration comes from Billy, the milkman. Billy is in love with Eva, and his stories—derived from the milkman’s own daydreams—complicate the investigation even further. Eva, in turn, feeds the scheme with half-truths and clues that float between truth and theater, weaving a narrative that both entices and misleads.
Back at his own home, Molyneux hunts for threads of evidence, while Eva, in Chinatown, captures the attention of William Kramps with flowers and flattery. When Molyneux arrives and reveals to Kramps that he is the writer Felix Chapel, and that the woman nearby is the missing Mrs. Molyneux, the two men share a drunken, conspiratorial bond and stumble back to the Molyneux residence. There they encounter Soper, disguised as a kilted Scottish soldier, desperately trying to recover an incriminating signed photo of a showgirl left behind, and a sleeping detective who—like the city itself—has been drinking too much.
Outside, a furious crowd gathers, eager to hang the bishop for the alleged murder of Mrs. Molyneux. Mrs. Molyneux herself slips through the garden to discover William Kramps sleeping, naked, beside the pond. Her husband, now present in the house, advises her to hide in a closet for safety. The sleeping detective, awakened by the commotion, confesses that the body was revealed to him in a dream, and when the closet is opened, Mrs. Molyneux is found safe but under threat. Kramps returns, claiming he has killed Mr. Molyneux and is quickly arrested, though he vows to escape. In the end, the irritable chaos resolves with Molyneux choosing to remain as Felix Chapel, because the persona is better paid and more entertaining than reality.
Throughout these capers, the world surrounding the Molyneuxs—Margaret Molyneux, Françoise Rosay; Elisabeth Soper, Annie Cariel; and the others who drift between rooms, secrets, and rumors—remains a mosaic of social performance and misdirection, where deception, affection, and danger blur into a single, sprawling London night.
