A stage performance turns lethal when a prop gun fires real bullets, forcing Inspector Roderick Alleyn to investigate a cast of suspects hiding behind their theatrical personas. The protagonist, Inspector Alleyn, must navigate the insular and ego-driven world of the Unicorn Theatre to uncover how a harmless prop was replaced with a deadly weapon. He faces a group of actors who are adept at deception, making the truth difficult to discern amidst their rehearsed performances. The narrative follows a traditional investigative framework, focusing on the meticulous collection of clues and the psychological interrogation of the suspects within the confines of the theater.

This work is widely regarded as a quintessential example of the Golden Age detective novel, showcasing the author's ability to blend theatrical flair with rigorous procedural logic. Readers often highlight the atmospheric setting of the London stage as a key strength that elevates the central mystery. The character of Inspector Alleyn is frequently praised for his understated intelligence and calm demeanor in the face of dramatic personalities. The narrative structure is noted for its precision, providing a satisfying puzzle that rewards careful attention to detail. The book remains a staple for those who appreciate the classic British mystery tradition and its focus on character-driven deduction.