In Biggles Hunts Big Game, Stephan was an operative of the counterfeiting gang led by Kravas. Stephan was a wartime associate of the gang's master forger Dr Dorov, working with the doctor when he was in charge of Hitler's forgery and counterfeiting department. After the war, Stephan had joined the gang along with Dorov and was employed as a mechanic, working at the printing shop which the gang maintained at their hunting-lodge at Kudinga.
Towards the end of the book, as the managers of the gang feared that Biggles was closing in, the manager at the lodge, Kreeze, ordered Stephan and his fellow mechanic George to sink the printing shop, which had been built in a watertight building on pontoons on a lake. This would remove any evidence from the eyes of the police. However, after opening the valves to flood the pontoons, Bertie, who was trapped inside the printing shop fired some shots. George feared this might have punctured the walls or roof of the building and thus closed the valves to stop the flooding process and went back to report to Kreeze leaving Stephan at the power house.
When Biggles arrived at the print shop with Tug, Stephan assumed they were fellow members of the gang. Tug, whose cover as Kravas' pilot had not been blown yet, told Stephan that Kravas was highly annoyed and ordered him to refloat the pontoons and haul the print shop in because the gang bosses wanted to speak to the people who were trapped inside. Stephan compiled, but he became suspicious when he saw a large group of people running from the lodge towards the power house, shouting and occasionally firing warning shots. Stephan tried to draw his gun but Biggles pointed his gun at him and warned him to keep still. Stephan tried to break away but lost his footing outside the power house and fell into the lake which was full of crocodiles. According to John's text, "there was a vicious swirl" and a "great gnarled tail broke the surface for a moment before gliding into the depths." Stephan was never seen again.