In 1943, a group of Allied POWs who have repeatedly escaped from camps across the Third Reich are moved to a new camp under the command of Luftwaffe Colonel von Luger. He warns British Group Captain Ramsey—the highest-ranked POW officer and their de facto leader—that any man who escapes will be shot. Privately von Luger opposes such measures, but the Gestapo, tired of the disruption caused by breakouts elsewhere, has threatened to intervene if the Luftwaffe cannot stop them for good.
Several prisoners ignore the threat and attempt to escape on the first day, but none make it past the fence. USAAF Captain Hilts, a notoriously prolific escapee, notices a blind spot at the fence—however, he purposefully gets caught before the guards can realize his discovery. Sentenced to solitary isolation (“the cooler”[9]), he befriends RAF Flying Officer Ives, who is also eager to escape.
RAF Squadron Leader Roger Bartlett re-establishes "the X Organisation", the escape-planning committee at their former camp, with Ramsey's tacit approval. He argues that their best way to help the Allied forces is to break out an unprecedented 250 men simultaneously, forcing the Germans to divert significant manpower away from the front.
The POWs begin working on three tunnels: "Tom", "Dick", and "Harry". Hendley secures vital objects on the black market, and forms a bond with expert forger Blythe. Sedgwick makes picks and air bellows, Welinski and Dickes oversee the digging, MacDonald gathers intelligence, Griffith sews civilian disguises, and Ashley-Pitt devises a method of hiding the excavated dirt. Digging noise is masked by a choir, led by Cavendish, who also surveys the tunnels' routes.
Aware that Hilts is planning to jump the fence, Bartlett asks him to scout out the surrounding area and then allow himself to be recaptured so he can draw maps for the X Organisation. Hilts refuses out of pride.
When "Tom" nears completion first, Bartlett orders "Dick" and "Harry" sealed off. Hilts, Hendley, and Goff brew potato moonshine with a homemade still and celebrate the Fourth of July with the camp, but the guards accidentally find "Tom" mid-party. A despondent Ives snaps, frantically climbs the fence, and is shot dead. Hilts, shaken, agrees to Bartlett's proposal.
Bartlett orders "Harry" reopened. When the tunnel partially collapses, Welinski breaks down and confides to Dickes that he is claustrophobic. He tries to climb the fence like Ives, but Dickes manages to calm him down and prevent him being shot. Blythe finds he is going blind due to progressive myopia, and Hendley takes it upon himself to be Blythe's eyes during the escape.
They complete "Harry", but on the night of the escape they break to the surface and find themselves 20 feet short of the forest, and still within sight of the guards. Guided by Hilts tugging on a rope as a signal—and aided by a fortuitous air raid blackout—dozens of men flee before Cavendish slips and makes a noise. An impatient Griffith surfaces while a guard investigates and is captured, ending the breakout.
The 76 escapees flee throughout Europe. Welinski and Dickes row to a port and board a ship for Sweden, while Sedgwick cycles to France, where the Resistance smuggles him to Spain. The rest are unsuccessful: Cavendish hitches a ride on a truck, but is turned in by the driver. Hilts steals a motorcycle and heads for the German-Swiss border, chased by soldiers, but after jumping one line of tank barriers his bike is shot and he is recaptured. Hendley and Blythe steal a Luftwaffe training plane to fly to Switzerland, but crash when the engine fails; Blythe is shot and Hendley recaptured. At a railway station Kuhn, a Gestapo guard from the camp, helps search among the disembarking passengers for escapees; Ashley-Pitt kills him to prevent him recognizing Bartlett, and is then also shot dead. However, Bartlett and MacDonald are still caught when another Gestapo officer tricks MacDonald into speaking English while boarding a bus.
Fifty of the men are loaded into trucks, taken to a field, and shot dead on Hitler's direct orders. Hendley, hearing the news on his return to the camp with the survivors, asks Ramsey if the escape was worth it. Von Luger, ashamed by the murders, is relieved of command by the Gestapo and driven away to an uncertain fate—but as he leaves he tells Hilts that it looks like the American will be the one who gets to see Berlin first. Hilts is sent to the cooler, where he begins planning his next escape.
