August, 1943. Colonel Joseph Ryan of the US Army Air Forces is shot down in Italy and taken to a prison camp populated by the Royal Army's 9th Fusiliers and run by sadistic commandant Battaglia. With the recent passing of their commanding colonel, the 9th Fusiliers under Major Eric Fincham must now answer to the new senior officer of the prisoners, Ryan. Also in the camp are several American prisoners who don't cotton to Major Fincham's stubborn passive resistance to Battaglia, passive resistance that has led to denial of clean clothes, soap, running water, and decent food. When two of the Americans are "arrested" by Fincham for trying to steal medicines being horded for escape attempts, Ryan points out the varied tunnels being built by Fincham's men to Battaglia in exchange for necessities, but is double-crossed by Battaglia. Ryan then fights back with an audacious order, which embarasses Battaglia and sends Ryan to a sweatbox to die. But Italy surrenders a few days later and Battaglia is taken prisoner and put to trial in which he will be executed, even though with Italy out of the war he is now a civilian. Ryan disbands the trial and has Battaglia placed in the sweatbox, but a German overflight forces the battalion to flee for safety. After a day-night march, the escaped prisoners and trapped by German forces and herded onto a train, but not before their betrayer can stand and gloat at his victory, and earn Ryan seemingly permanent hatred by the British soldiers. Ryan, however, is not finished, and orchestrates an even more daring escape, seizing the train. But with German forces all around, and after escaping a bombing raid by British Lancasters, they must drive the train further north to escape the Germans and try for the only safe haven to be found.

Trevor Howard was second choice for Major Fincham.

Maj. Eric Fincham:
I once told you Ryan, if only one gets out, it's a victory.

Factual errors: Sunbeams cannot shine simultaneously into the boxcar from opposite sides.