The Novel Within 12 Hours by the Norwegian writer Peter Valentin (a nom de plume of Waldemar Brøgger) was published in Stockholm in 1944 by Bonniers. Owing to the looming conflict between the Swedish government and the film industry over the entertainment tax (see also Summer Interlude), Svensk Filmindustri was keen to produce an internationally viable success in the form of a spy thriller. Herbert Grevenius was commissioned to write the screenplay, and Ingmar Bergman, "for financial reasons", undertook the task of directing. It turned out to be a painful experience all round.

Read more in Shooting the film