In 1944, a handsome bachelor and nuclear physicist named Alvah Jesper is working in the United States on the Manhattan Project to build a nuclear bomb. Recruited into the Office of Strategic Services, his mission is to make contact with a Hungarian nuclear physicist, Katerin Lodor, who has been working on the German project to make a nuclear bomb and has escaped into neutral Switzerland. Flown into Switzerland, Alvah finds it full of German agents who, after he manages one brief conversation with Katerin, abduct her. By befriending and then blackmailing Ann Dawson, an attractive American now a German agent, he discovers where Katerin is being held, but an OSS raid on the building fails and she is shot dead.