The new Comet was fully expected to be the sensation of the annual Motor Show at Olympia. Suddenly, in the middle of the dense crowd of eager spectators, an elderly man lurched forward and collapsed, apparently in a dead faint. But Nahum Pershore had not fainted. He was dead, and it was his death that was to provide the real sensation of the show.

A post-mortem revealed no visible wound, no serious organic disorder, no evidence of poison. Doctors and detectives were equally baffled, and the more they investigated, the more insoluble the puzzle became. Even Dr Lancelot Priestley’s unrivalled powers of deduction were struggling to solve this case.