After American Paul Martin rescues Kathe Solotkin from Latvia, a country behind the Iron Curtain, they flee by fishing boat to the Danish island of Bornholm in the Baltic Sea. Kathe's escape was engineered, in America, by her grandparents, who also reared Paul. Because Paul was spotted in Latvia taking photographs of a rocket-launching site, the authorities send Petrov, a Russian secret agent for the Ministry of Internal Affairs (MVD) to apprehend the couple. On Bornholm, a priest introduces Paul and Kathe to Lee Brooks, an American nightclub singer on her way to an engagement in Copenhagen, and she agrees to take them there. Petrov follows the trio onto the ferry to Copenhagen and, after discovering a letter in Lee's car from a friend at the American Embassy in Paris, introduces himself to Lee as a colleague of the official. Petrov tells Lee, in confidence, that Paul is a member of the Russian secret police and is in possession of information highly dangerous to the United States. When Lee protests that it appears very unlikely that Paul could be a Russian, Petrov informs her that Paul is a highly trained agent, capable of posing as a Swiss, a Dane or an American. Petrov then asks Lee to keep Paul and Kathe occupied on deck, giving him a chance to search their staterooms. Lee agrees to help Petrov and, the next morning, invites Paul and Kathe to join her for coffee on deck as the ship approaches the Copenhagen harbor. After Lee, who is apolitical, tells Paul that an American Embassy official has accused him of being a Communist, Paul realizes that they are being followed, goes to Kathe's stateroom and surprises Petrov. The Russian escapes by jumping overboard after slugging Lee, who apologizes to Paul and Kathe for having been so gullible. Petrov has not found Paul's film, however, and Lee agrees to drive Paul and Kathe to a church where they are to hand it over to a member of the underground. Meanwhile in a dockside warehouse, Colonel Touchenko, Petrov's superior who has followed him to Copenhagen, interrogates him about the whereabouts of the film. When Petrov is unable to produce it, Touchenko accuses him of dereliction of duty and treason. Touchenko also states that the twenty years Petrov spent in America have caused him to forget everything the Party taught him and have planted seeds of decadence in him. After Touchenko suggests that Petrov's failure might be deliberate, Petrov begs for a few more hours to locate the film. Touchenko then informs him that he already knows that Paul and Kathe are at the church. There, the contact man informs Paul that he is to deliver the film to a man who operates pony rides at the Tivoli amusement park. Concealing the film in a belt, Paul asks a young boy to give it to the man operating pony rides. Petrov eventually catches up with Paul in the tower of a seventeenth-century church, but in a surprising confrontation, tells Paul that he, as a loyal MVD agent, could easily have killed him earlier but chose not to. Petrov then reveals that there were two things he wanted to get out of Latvia, the film and himself. Intending to defect, Petrov shows Paul a highly important document he intends to turn over to the U.S. embassy detailing the exact distances between every military objective in the Soviet Union and the United States. After Petrov advises Paul that Touchenko, the most feared man in the MVD, is now after both of them, he advises him to collect Kathe from her hotel and leave Denmark immediately. After thanking Lee for her help, Mike and Kathe board a flight for New York.
