Tommy and Tuppence have a chance encounter on a train with an agitated young woman who suddenly disappears and never returns to her seat.

Tommy and Tuppence's search for the missing Jane Finn gets more dangerous. Tommy finds himself being mistaken for a criminal mastermind whilst Tuppence is employed as a maid to faded soprano Rita Vandemeyer, who has some suspicious connections to Brown. The couple find their investigations getting deeper and even more dangerous.

The Beresfords search for Jane Finn comes to a close, as they uncover the identity of Mr. Brown.

Tommy and Tuppence are enlisted to find a Soviet agent and a kidnapped scientist.

Tommy and Tuppence turn their attention to their fellow occupants of Sans Souci to find N.

Tommy and Tuppence must come up with their most ambitious and risky plan yet.