At age 34, Army Air Force pilot Major Robert Lee Scott Jr. (Dennis Morgan) is considered too old to fly in combat, but he is recruited and volunteers to fly in a secret bombing mission from the Philippines against Tokyo, the Japanese capital. When the mission is cancelled after his arrival in India, due to the fall of the Philippines, Scott is promoted to Colonel and assigned to fly transport aircraft on dangerous, unescorted missions over The Hump from Burma to China. These flights supply aviation gasoline and other much-needed supplies to the three squadrons of the American Volunteer Group, the Flying Tigers.