In 1943, a contingent of Allied POWs, infamous for their repeated escape attempts from various camps throughout the Third Reich, finds themselves relocated to a new facility under the stern command of Luftwaffe Colonel von Luger. He forewarns the British Group Captain Ramsey, who is the highest-ranking officer among the POWs and serves as their de facto leader, that any escape will result in execution. Behind closed doors, von Luger is opposed to such extreme measures, yet the Gestapo—frustrated by the escalating chaos due to breakouts—threatens intervention if the Luftwaffe cannot effectively put an end to the escapes.
On the very first day, a few prisoners disregard the grim warning and attempt to escape, but they all fail. Among them is Hilts, a notorious escape artist, who keenly observes a blind spot in the camp's fencing system and intentionally gets captured before the guards can detect his discovery. After being sentenced to "the cooler," he is confined in a cell adjacent to Ives, and the two form a friendship amidst the confines of their captivity.
RAF Squadron Leader Roger Bartlett takes the initiative to revive "the X Organisation," a committee dedicated to planning escapes, with Ramsey's unspoken consent. He passionately argues that they could disrupt the German war effort significantly by breaking out an unprecedented 250 men at once, thereby forcing the German army to redirect essential resources away from the front lines.
As the prisoners’ resolve strengthens, they embark on constructing three tunnels named "Tom", "Dick", and "Harry." Hendley cleverly acquires essential tools through the black market and builds a partnership with the master forger Blythe. Meanwhile, Sedgwick assembles tools for digging, while Welinski and Dickes supervise labor efforts. MacDonald collects intelligence, Griffith stitches civilian disguises, and Ashley-Pitt devises a strategy for concealing the displaced dirt. Their mining activities are cleverly masked by a choir led by Cavendish, who is also tasked with monitoring the tunnels' routes. Recognizing Hilts' intentions of jumping the fence, Bartlett asks him to survey the surroundings before voluntarily getting recaptured to aid in their plans. However, Hilts refuses out of sheer pride.
When "Tom" nears completion first, Bartlett instructs that "Dick" and "Harry" be sealed off. In a moment of camaraderie, Hilts, Hendley, and Goff celebrate Independence Day with homemade potato moonshine, but their revelry is abruptly cut short as the guards unexpectedly discover "Tom." Overcome with despair, Ives frantically attempts to scale the fence, only to be shot dead. The traumatic event leaves Hilts stirred, leading him to reluctantly accept Bartlett's strategy.
Bartlett then decides to reopen "Harry." However, when the tunnel partially collapses, Welinski breaks down, admitting his claustrophobia to Dickes. As he attempts to escape like Ives, Dickes manages to diffuse the situation and prevent another tragedy. Meanwhile, Blythe faces an alarming reality as he discovers he is going blind, prompting Hendley to assist him as they plan their escape.
With "Harry" finally complete, the night of the breakout arrives, but the prisoners are shocked to find themselves just 20 feet short of the safety of the forest, still exposed to the guards’ line of sight. Under Hilts' guidance, who signals the group with a rope, and aided by the momentary blackout from a nearby air raid, dozens of men flee. Yet chaos ensues when Cavendish slips and stirs suspicion. An eager Griffith surfaces to investigate but is swiftly captured, leading to the unraveling of their carefully orchestrated plan.
The prisoners scatter across Europe in a desperate search for freedom. Welinski and Dickes successfully row to safety and board a ship bound for Sweden, while Sedgwick cycles towards France, ultimately relying on the Resistance to smuggle him into Spain. Regrettably, many others meet with failure: Cavendish attempts to hitch a ride only to be betrayed by the driver, Hilts commandeers a motorcycle in a daring escape towards the German-Swiss border, but after a thrilling chase where he jumps over tank barriers, he is recaptured. Hendley and Blythe steal a Luftwaffe training plane in a bid for survival but plummet when their engine fails; Blythe is shot, and Hendley is apprehended again. At a train station, Ashley-Pitt eliminates a Gestapo guard to protect Bartlett, only to be shot himself in the process. Ultimately, Bartlett and MacDonald are caught when a Gestapo officer tricks MacDonald into revealing his identity.
Fifty prisoners, including Bartlett, MacDonald, and Cavendish, are rounded up, transported to a field, and executed under Hitler's direct orders. Seventeen return to the camp, while six are sent to death camps.
Upon his return, Hendley, hearing of the grim news, questions Ramsey if their daring escape was worthwhile. Meanwhile, von Luger, burdened by the shame of the executions, loses his command and is driven away, facing an uncertain fate. Before he departs, he poignantly informs Hilts that it seems he will be the one to see Berlin first. Now facing confinement in the cooler once more, Hilts begins plotting his next escape, determined as ever.
