While traveling by train, Tommy and Tuppence found themselves sharing a carriage with a visibly distressed young woman. Suddenly, she vanished—departing without a trace and leaving her seat unoccupied.

To infiltrate their adversary’s circle, Tommy assumed the guise of one of Brown’s associates, while Tuppence secured a position as a housemaid in the service of a man they suspected might be involved.

The Beresfords' pursuit of Jane Finn finally concludes with the revelation of Mr. Brown’s true identity.

Tommy received a clandestine assignment: to uncover the identity of a Soviet agent residing within a quiet seaside guest-house. Naturally, Tuppence refused to remain sidelined and insisted on accompanying him.

Turning their focus now to the other residents of Sans Souci, Tommy and Tuppence began searching for N.

At long last, Tommy located the vanished scientist, yet now they are both prisoners of M, and the identity of N remains a complete mystery.