A weekend house party gathers a group of bright young people at Chimneys, the grand country estate now leased to the self-made Sir Oswald Coote and his wife. When the guests devise a harmless prank to embarrass a notoriously heavy sleeper, the joke curdles into tragedy: Gerry Wade is found dead, apparently from an overdose of sleeping draught, with seven alarm clocks arranged in his room. The verdict of misadventure satisfies almost everyone, but a second death and a dying man's reference to the Seven Dials convince Lady Eileen Brent, known to all as Bundle, that something far darker is at work. Refusing to leave the matter to the official inquiry, Bundle teams up with the young men of her circle and follows the trail from her father's house to a Soho cellar where hooded figures meet in secret. Behind the conspiracy lies a plot to steal a closely guarded invention before it can be handed to the British government. As Bundle pieces together the link between the clocks, the deaths and the masked society, the imperturbable Superintendent Battle moves through the case in his own quiet way. Christie blends country-house comedy with espionage adventure, setting wit and high spirits against genuine danger. The result is a fast, playful puzzle in which charm and suspicion are difficult to tell apart, and in which the spirited heroine must decide which of her companions can be trusted.