Sebastian is an undisciplined mathematics genius who works in the "cipher bureau" of the British Intelligence. While cracking enemy codes, Sebastian finds time to romance co-worker Rebecca Howard.

Dirk Bogarde
as Sebastian

Susannah York
as Rebecca Howard

Lilli Palmer
as Elsa Shahn

John Gielgud
as Head of Intelligence

Janet Munro
as Carol Fancy

Ronald Fraser
as Toby

Margaret Johnston
as Miss Elliott

Nigel Davenport
as Gen. Phillips

John Ronane
as Jameson

Hayward Morse
as Gavin