An American scientist is sent by the CIA to East Germany to retrieve a secret microfilm from a Soviet scientist interested in defecting to the West but the Stasi secret police's surveillance complicates matters.

Montgomery Clift
as Professor James Bower

Hardy Krüger
as Counselor Peter Heinzmann

Macha Méril
as Frieda Hoffmann

David Opatoshu
as Orlovsky

Christine Delaroche
as Ingrid Weiß

Hannes Messemer
as Dr. Saltzer

Karl Lieffen
as Major Windisch

Uta Levka
as Mädchen unter der Dusche

Roddy McDowall
as Agent Adams

Johannes Buzalski
as Agent (uncredited)