Joy is a thief who is attempting to obtain a film that was to premiere at a film festival. The film shows some American spies making a drop at a location behind the Iron Curtain. It was filmed by Lester V. Griffin (Noel Harrison), who has refused to sell the film, even to American Intelligant sources.
Alexander Mundy (Robert Wagner) shows up posing as an author to get the film. Joy is first seen at an outside restaurant at the table of Griffin. Mundy sits near by, and makes conversation with Griffin, who is intrigued by him.
At a costume ball being held at the hotel, Joy appears as a magician assistant to Griffin, who is a magician. Both are wearing costume eye masks.
When Mundy and Griffin go off to talk about the film, Joy shows up with her goon, Paco (Nate Esformes). The two hold pistols at Griffin, and demand to know the whereabouts of the film, that she has already paid for. The lights go out, and Mundy escapes. In the commotion, Paco shoots Griffin in the arm, and Joy chases after Mundy.
Later, Joy demands Mundy get into her convertible car at gunpoint. Mundy is able to disarm Joy with a kiss, and tells her that she is not made for this business. However, Joy has a hidden pistol and follows Mundy into a film studio, where he unlocks the safe to a film vault. Joy is about to grab the film for herself, when another chase takes place.
The film is made worthless by dropping in acid. As a result, the part in the film where the American spies are uncovered is ruined. Joy shows up along with spy, Iris Vander (Amy Thomson), who originally had been tied up by Mundy. Joy tells Mundy that she has given serious thought about getting out of the business.
Later at the film festival, Joy and Iris show up and tell Mundy that they are ready to defect to the U.S. They go arm and arm with Mundy into the theater.