In this espionage thriller, Dan Slater (Yul Brynner) is a CIA agent who travels to Austria after his son dies in a skiiing mishap. Slater begins to suspect that his son's death wasn't an accident and begins investigating the matter on his own. Slater finds that fellow agent Frank Wheatley (Clive Revill) is of little help to him. Beautiful Gina (Britt Ekland), the companion of prominent socialite Mrs. Carrington (Moira Lister), then slowly draws Slater into her web. In time, he discovers that his son's death was all part of a diabolical plan to lure him to Austria; Soviet agents led by Bethold (Anton Diffring) have performed extensive plastic surgery on one of their top spies until he's identical to Slater, and they intend to send him back in Slater's place, giving them an insider at the highest levels of U.S. intelligence.