Several murders of nuclear scientists, that baffles Scotland Yard, occur in London around the same time that Bill Locklin, a special officer from the United States State Department, arrives to oversee the transfer of Professor Leon Dushenko, a Russian scientist who has fled the USSR. An attempt on Dushenko's life is made with a monkey's paw-print found at the scene.

Warned that it is haunted, a skeptical young couple buy a rundown yacht and fix it up to be their home-on-the-sea, only to slowly realize that it really is haunted.