Intended for an international audience, all dialogue is in English even though the film takes place in Sweden. Apart from Hardy Krüger as scientist Mandell all Swedish characters are played by Swedish actors.
This espionage film presents a character named Stig Larsson, which sounds quite similar to the real-life name of future known author Stieg Larsson, best known for The Millenium trilogy, which also deals with themes of espionage.