A Swiss Bank president hires an American investigator to ferret out a group of blackmailers that have been terrorizing his clients. Meanwhile, American gangsters hit the streets of Zurich with the intention of killing a Chicago mob figure, who happens to be one of the blackmail victims. Other blackmail victims include a beautiful Zurish resident, a Texas businessman, and a wealthy Dutchman. The investigator (David Janssen) identifies four potential suspects, including the bank vice-president's mistress (Elke Sommer). Adding to the intrigue is that the Swiss Federal Police are suspicious of the American and are soon making his job more difficult. Ultimately, the investigation leads to the bank paying the chief blackmailer in uncut diamonds, which results in a dramatic showdown in the snow-covered Alps and a surprise revelation. The cast also includes John Saxon, John Ireland, Senta Berger, and Ray Milland.