After John Sullivan's troopship is sunk in 1942, he is saved by Yugoslav Chetniks, whose leader Marko forces John to travel with him up through Greek Macedonia to a village where he has to practice as a doctor. Trapped with the Chetniks for nearly three years, his greatest desire is to meet with English stationed not far away but is always thwarted in his efforts. During his escape from the Chetniks he rescues a Jewish girl, Nadia, who he falls in love with. Soon they are both taken by Communist Partisans who continue to keep him isolated. John resolves to stay with the Partisans but when a dying British commando asks him to get an urgent message to a specific officer in London regarding Overlord, he does all he has to do to complete the mission of the commando with dramatic results.