Set in a somewhat fictionalised version of the true story, the film centers on Stalag Luft III — the POW camp where the real Great Escape events took place, though this tale follows a different compound — and focuses on inmates Williams, Michael Codner, and Oliver Philpot. In both the book and the film, the escapees are renamed Flight Lieutenant Peter Howard, Captain John Clinton, and Philip Rowe.
The prisoners face a daunting challenge: digging an escape tunnel while the entrance must remain hidden from a distance that reaches the perimeter fence. They devise a clever plan to carve out a tunnel whose entrance sits in the middle of an open area near the fence, concealed by a vaulting horse—a lightweight structure built largely from plywood supplied by Canadian Red Cross parcels. The team forms a process where each day they haul the horse to a fixed spot, with a man hidden inside. Beneath the horse, the digger works, carefully placing wooden boards cut to fit the aperture and filling the hollow with sandbags and dry sand to mask the digging. The goal is to keep the surface level and the earth quiet, as wet sand—darker in color—would betray their activity.
As the tunnel grows longer, the operation becomes more complex: two men hide inside the horse while a larger group exercises above, creating a convincing routine. At the end of each session, the entrance is sealed again and everyone retreats to their hut, the tunnel concealed beneath the moving silhouette of the horse. A third man is recruited to help, a role that Phil reluctantly accepts with the promise that he will join the escape.
When the breakout finally comes, Captain John Clinton hides in the tunnel during an Appell (roll call) before three men are carried out in the horse—the third man stepping in to replace the tunnel trap. Howard and Clinton then travel by train toward the Baltic port of Lübeck, though in reality they move via Frankfurt an der Oder to Stettin. Phil elects to travel alone, posing as a Norwegian margarine salesman and moving by train through Danzig to neutral territory. The odds are perilous at every turn.
On the docks, Howard and Clinton are forced to kill a German sentry who discovers the hiding men. With danger close behind, they contact French workers and meet Sigmund, a Danish resistance collaborator who guides them onto a Danish ship. They transfer to a fishing boat, arrive in Copenhagen, and are eventually shipped to neutral Sweden, where they are reunited with Phil, who had arrived earlier.
Not all details from Williams' book found their way into the film, and some aspects of the broader escape story were omitted. For instance, the book mentions the possibility of visiting potentially neutral brothels in Germany, an idea that was abandoned for fear of a trap. The film stays focused on the nerve-wracking plan, the meticulous work beneath the surface, and the fraught journeys to safety, all while maintaining a grounded, documentary feel that underscores the courage and ingenuity of those involved.
