A house-party with a glittering guest-list. An imposing country estate with endless shadowy staircases and unused rooms. The breathless period between the two world wars. It's the ideal setting for the classic English murder mystery, and bringing it to perfection is the introduction - in a supporting role, for the first and last time - of Albert Campion, the consummate (if compulsively quipping) Gentleman Sleuth. The guests take some time to be grateful...