It was a very strange sort of a party at Tudor Arches, twelve guests, each masked, each unknown to the other, and each with a dark secret. Their host, if anything, was even stranger, a mysterious figure who had been blackmailing his guests for years, but who had called the party to announce that he was getting out of the blackmail business and was restoring the incriminating evidence to his guests. But things take an even stranger turn when the host is poisoned within moments of revealing his plans. Thus begins one of the strangest cases in Inspector Anthony Slade's career at Scotland Yard's Criminal Investigation Department.