When that extraordinary couple, Tommy and Tuppence Beresford, take over a near-bankrupt detective agency, they are warned by the Secret Service that the agency itself might be an information drop for Russian spies. Tommy and Tuppence are ever on the lookout for clues to uncover a Bolshevik conspiracy, but meanwhile they solve case after case, each time assuming the methods and even the personalities of such great fictional detectives as Sherlock Holmes—and Hercule Poirot!