The scene is London, England, in the mid-nineteen twenties. Private detectives Melpomene and Alex are asked to investigate problems at a London stock-broking firm. Soon it becomes clear that certain officers of a prominent embassy are also involved in extensive illegal money transfers with European countries financing the arms and drug-running trades. Before long there have been killings and Crabbe and Crabbe are warned off by anonymous letters and telephone calls - of course they are not daunted and the guilty are brought to account, with the cooperation of the authorities.