Character of Ladeynikov played by Donatas Banionis was heavily inspired by an actual Soviet spy Konon Trofimovich Molody. Just like in the movie he was caught and then imprisoned for 3 years and later exchanged for another spy held by Soviets. Konon Molody acted as a consultant on a movie and insisted that his character should be played by Donatas Banionis, mainly because of the physical resemblance. Before that Vyacheslav Tikhonov was cast to play his role.