In post-war Turkey, former O.S.S. operative Steve Roark is still involved in espionage activities and occasionally functions as a double agent for the Russians. He is assisted in his activities by suave Turk, Ali Imagu. Steve receives a message that Austrians Linda Carlson and Dr. Eric Viertel are in Sofia, Bulgaria. Steve also learns that Linda, with whom he fell in love during the war and thought had been killed by the Germans, and Viertel were working on atomic research when the Nazis captured them and sent them to a concentration camp. The Russians liberated them and encouraged their research, sending them to Sofia to interest other scientists in working on the same research. Steve finds it hard to believe that Linda would willingly work against the interests of world peace, but agrees to help them escape to America. In order to obtain papers to go to Sofia, Steve agrees to work with ex-Nazi Peter Goltzen and Rumanian nightclub singer Magda Onescu, who is attracted to him, in arranging the escape of a Russian political prisoner from an Istanbul jail. After Steve and Ali free the prisoner and get him to Sofia, they are given papers enabling them to remain there. Steve is shocked to learn that Linda has married Viertel, as he is still very much in love with her. Steve seeks help from Dr. Stoyan, one of the leaders of the Balkan underground, who is attempting to set up an independent coalition of democratic states. To convince Stoyan of his integrity, Steve tells him that, during the war, he, Linda and Viertel hid in a mountain chalet in Austria and photographed important atomic research papers for the Americans. However, Stoyan cannot promise to assist Steve in getting Linda and Viertel out of Bulgaria and, ultimately, has to refuse to help as this could jeopardize his compatriots' activities. Meanwhile, Goltzen, who is working for Russian agent Ana Sokolova, kidnaps Linda and Viertel and puts them on a private plane to Vienna. However, Steve and Ali manage to take over the plane and deliver them to safety in Salonika, Greece. Steve and Ali return to Sofia, where Magda furnishes them with an alibi for their absence. In Athens, meanwhile, Goltzen's agents shoot and kill Viertel and Linda is tricked into returning to Sofia. After Goltzen and Sokolov capture and torture Steve and Linda to reveal the atomic secrets, Ali pleads with Stoyan to help free them. With Stoyan's help, Ali engineers Steve and Linda's escape, during which Goltzen is killed and Sokolov captured. Their mission accomplished, Steve and Linda head for America.