An elderly man collapses and dies in the middle of a dense crowd at Olympia's Motor Show, baffling doctors and detectives alike. Nahum Pershore's death, seemingly without cause, presents an insoluble puzzle to the authorities. Dr. Lancelot Priestley, renowned for his deductive skills, finds himself challenged by the lack of visible wounds, organic disorders, or poison. The investigation into this seemingly impossible murder unfolds amidst the bustling atmosphere of the motor show, where the killer could have easily blended in.

This classic mystery novel by John Rhode, also known as Cecil John Charles Street, is recognized for its intricate plotting and cerebral puzzles. Rhode, a prolific author in the Golden Age of Detective Fiction, was known for his focus on 'fair play' mysteries where all clues are presented to the reader. The novel likely appeals to readers who enjoy traditional detective stories with a strong emphasis on logical deduction and a challenging central enigma. The reception of such works typically centers on the cleverness of the solution and the author's skill in misdirecting the reader while adhering to the genre's conventions.