During World War II, US Army First Lieutenant Thomas Hart (Farrell) is captured by German forces during the Battle of the Bulge. He is sent to a prison camp, where he encounters the social and physical struggles of POWs.

As Hart is moved to the camp a P-51 starts to shoot at them and the guards, thinking them all to be Germans (POW was painted on the top of the train but got covered by thick snow.) They are able to get out but a person is killed getting the train door open. To save themselves, the POWs begin to spell P-O-W with their bodies and manage to lead the P-51 away.

As a high ranked officer, Lt. Hart is introduced around the camp by a few men. He learns about the execution of many who tried to escape or broke the rules of the camp. He is also well known by German officers.

Two black pilots are brought to the camp; they are the only blacks among the white POWs. One is soon executed by being accused of keeping a weapon (the racist Staff Sgt. Vic W. Bedford placed a weapon in his bunk) and the other accused of killing the afore mentioned sergeant in revenge. A law-student before the war, Hart is appointed by Army Col. William McNamara (Willis) to defend the accused pilot at his court-martial (where German officers cooperate with the court). Only much later does McNamara reveal that the "defense," like the trial itself, is to be a sham, an elaborate distraction to hide a planned escape by McNamara and his men. The film ends with the escaped soldiers destroying a nearby ammunition plant and the colonel voluntarily returning to the camp to take all the punishment. Oberst Visser (Iures), the German officer responsible for the camp, decides not to slaughter the prisoners, instead shooting McNamara in the head, killing him instantly.

Three months later, the German army surrenders to the Allies. The prison camp is liberated and all of the prisoners, including Hart, are sent home