In 1920s London, six members of the Crime Circle set out to solve a murder that has baffled Scotland Yard. Equipped with all of the facts, as told to them by Chief Inspector Moresby, club president Roger Sheringham and his armchair detectives pool their collective talents to formulate theories about the death of Mrs. Joan Bendix by nitrobenzene poisoning. Over six successive nights, each member puts forward a plausible theory, but will any of them be able to reveal the truth?