After a chance meeting and an indiscreet conversation, childhood friends Tommy Beresford and Tuppence Cowley become involved in a convoluted intrigue led by a mysterious man known simply as Mr. Brown.

Francesca Annis
as Tuppence

James Warwick
as Tommy

Gavan O'Herlihy
as Julius P. Hersheimmer

Alec McCowen
as Sir James Peel Edgerton

Honor Blackman
as Rita Vandemeyer

Peter Barkworth
as Mr. Carter

Toria Fuller
as Jane Finn

John Fraser
as Kramenin

George Baker
as Whittington

Donald Houston
as Boris