In 1944, at a United States Army Air Forces {USAAF) air base in England, Capt. James M. "Steve" Stevens (Mark Stevens} and his Martin B-26 Marauder bomber crew are assigned to a second bombing mission of the day. The men are exhausted both physically and emotionally because the squadron has been repeatedly attacked by the enemy, possibly because someone has leaked information about the raids.

The men have been warned that the Germans have clever and insidious ways of extracting vital information from downed flyers. Over their target, however, their bomber is attacked and bombardier Russ Johnson (James Young) is killed. The rest of the crew, Steve, co-pilot Sgt. Frank Crawford (Johnny Sands) and gunners Sgt. Alfred Mitchell (Alex Nicol) and Sgt. Ralph G. Phelps (James Best) who is wounded, are forced to parachute out of the aircraft.

Steve and Al find each other on the ground but are promptly captured by German soldiers and brought to a "holding area" to prepare them for a German prisoner-of-war camp. There, they are greeted by a Red Cross representative, but Steve notices that the form asks for excessive information and both Americans refuse to fill it out.

Nazi intelligence officer Col. Von Broeck (Robert Douglas) then analyzes the little data he has and discovers clues to their personalities, including Steve's intelligence and Al's loyalty to Steve. Next, intelligence officer Capt. Fred Reiner (Gig Young), an American, visits Lt. Webster (Don Taylor), another prisoner, and, by lying that he is an Allied sympathizer has Webster reveal that Ralph is from Atlanta.

At the same time, a beautiful German nurse (Joyce Holden) tends the wounded Ralph, convincing him to fill out the fake Red Cross form and divulge that two new crews were added to the squadron recently. With this information, Von Broeck surmises that the Americans are planning a big bombing raid, pretending he will kill Steve unless Al tells more about the raid. Since raid is top secret, Al only reveals the kind of bombs to be used. After the fake firing squad, Von Broeck deduces the target must be one of four French cities, including Cambrai. Reiner interrogates Frank, who has been beaten by the Gestapo and brought to the intelligence station, and quickly discovers that from his list of possible targets it is the French town of Cambrai, where the Axis gasoline supply is stored,

Al, who has been assigned a cellmate overhearing him brag about what the Nazis have learned, and when the crew is reunited and about to be shipped out by train, a plan is hatched. With Al and Frank on the train, Steve and Al jump off the train but Frank is shot and killed by a guard.

The two fliers walk all night and come upon a French farmer, whose kind daughter sneaks them into the nearest city, outfits them in peasant clothing, and finds them a ride to a town near Cambrai that harbors French underground agents. Their driver Jean (Steven Geray) tells them about the gasoline supply at Cambrai being moved to another location.

The Americans find an underground bar, where an agent slips Al fake identification papers, but a singer tips off the Germans. Al is arrested but Steve escapes with the help of the agent and brought to the Underground headquarters, where he finally convinces the leader to send a warning to the Allies. As night falls, Steve and the Maquis leader see the American squadron flying away from Cambrai and realize the raid will succeed.