It's 1952, and Tommy and Tuppence Beresford, an ordinary married couple, are thrust into a web of international espionage after a chance encounter on a return train from Paris.

Tommy and Tuppence's search for Jane Finn, Brown's identity and the recording gets more dangerous as they struggle to maintain their cover.

The violent, criminal gang give Tommy a job to do after his cover is blown. Tuppence comes to his aid as they try to prevent an assassination.

The British Secret Service enlists Tommy and Tuppence's help again to find a Soviet agent and a kidnapped scientist.

Tommy and Tuppence turn their attention to the fellow occupants of Sans Souci to find N, the probable nuclear bomb thief.

Still none the wiser as to the identity of Soviet agent `N', Tommy and Tuppence must come up with their most ambitious and risky plan yet in order to protect the lives of British citizens.