In 1916, pilots Bob Wilson and Fred von Bergen, childhood best friends, test airplanes for an American company that builds bombers for the European allies. Because he is German-born, Fred loses his job and, unable to find other employment, decides to return to Germany to fight for his homeland. Although he has no special attachment to the German cause, Bob quits the airplane factory and joins his friend in Germany. On their way to a German airfield, Bob and Fred are accidentally run off the road by Red Cross nurse Alida Hoffman, who immediately catches the eye of playboy Bob and later impresses shy Fred. After Bob's first unsuccessful mission, Captain Wolters, the squadron's tyrannical leader, expresses his doubt about Bob's loyalty but, desperate for pilots, gives him another chance. However, when Bob chooses to make love to Alida instead of participating in a crucial air battle, Wolters, aware that the Americans have joined the Allies, arrests him. Fred, heartbroken that Alida has chosen Bob, quarrels with his friend and calls him a coward. Later, however, he allows him to escape from a firing squad and flee to the British forces. To prove his allegiance, Bob leads the British bombers to the German base, while Fred is told by Wolters that he must shoot down Bob to prove his loyalty. Neither man is capable of killing the other, and in the end, Fred sacrifices his life for Bob, who then returns to American with Alida.