Both David and Mariella Sheridan have become quite bored with their retirement so when Verlayne, international secret service agent for the League of Nations, asks for their help, they seize the chance. The mission is "to discover what men are at the back of various occurrences which have obviously been engineered by political interests. These include the murder of a British Agent stationed in Egypt, causing a brawl between Italian and British sailors in Alexandria, and the arrest of the PM's nephew on the charge of espionage.