Richard Widmark produced, co-directed and starred in this motion picture. It's both his first and last film he directed.
Many scenes were filmed in Zurich, Switzerland and Vienna, Austria with Vienna also standing-in for Budapest, Hungary.
Producer Euan Lloyd had been Richard Widmark's agent. Widmark would later help him out on Commando (1982) when Lloyd needed an American name to secure US distribution.
Senta Berger said this was her first major role and first American film. She was 18 when she met Richard Widmark, who was in Vienna casting for a leading lady. He spotted her riding a bike and eating an ice cream cone; her hair in braids. Widmark told her he was looking for a girl to play the part of an experienced woman. Berger didn't feel she looked the part, but when she auditioned, they dressed her in the proper clothing and makeup and it made all the difference.