Quiz

Gert Fröbe plays a man called "Steinhäger". In Germany Steinhäger is a alcoholic drink with a minimum of 38% ABV and is distilled in Steinhagen.

During the fake interrogation of Eddie Chapman in London, he is asked what film he saw in the movie theater. He answers; "Warsaw Concerto" with Anton Walbrook and Sally Gray." This could be an inside joke and reference to the film Dangerous Moonlight (1941) with participation of the mentioned actors and written by this film's director Terence Young.

The United Artists soundtrack album was arranged and conducted by Roland Shaw, but he did not work on the film's original score.

Terence Young, the director, knew Eddie Chapman from before the Second World War, and had met Chapman during his first "mission" to the UK.

This movie was loosely based on Eddie Chapman's autobiography. He was known as Agent Zigzag to British intelligence. The two principal exploits depicted in the film were reasonably accurate. He did successfully fake the destruction of the de Havilland aircraft factory (not the Vickers factory), and was instrumental in helping the British divert V-1 and V-2 rockets away from London into the countryside through his false reports. Much of the rest of the movie was fictionalized. Chapman himself was disappointed in the movie.