In southern Spain with a U.S. team, skydiver Fathom Harvill (Raquel Welch) is approached by Colonel Douglas Campbell (Ronald Fraser), who is working for a top-secret Western agency. He's after a vital lost atomic device, and wants her to parachute into a house occupied by some Red Chinese Agents to help get the thing back. Apart from all of this, there is a predatory continental doctor on his yacht to take account of. Fathom soon realizes nothing is what it seems to be.