Captured during the Spanish Civil War, John 'Kit' McKittrick (John Garfield) is held prisoner in a Fascist prison camp. The Nazis torture him in an attempt to locate a hidden flag, but Kit refuses to divulge its whereabouts. Upon his release Kit heads for America, but is followed by his former captors. The Nazis use psychological warfare to try and break Kit's resistance, employing the beautiful Toni Donne (Maureen O'Hara) in an attempt to wheedle the flag's location out of him. However, Kit decides to turn the tables and gain revenge for his years of imprisonment.