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.

A British psychiatrist reads an amnesiac's (Maxwell Reed) brain waves and sees the mind of a killer.

Someone knocked out a man and left him for dead during a fishing trip in Portugal. That someone is either his fetching wife, or two business partners, all sporting guilty faces after his unexpected return. Two more murders and a frame-up befall the quartet before an inspector closes the case.