During World War II, a group of Allied prisoners is held in a high-security German POW camp. The prisoners are an assembly of escape artists, each with a history of attempted breakouts and a determination to outwit their captors. Recognizing the need to work together to stage a mass escape, the group begins to plan a complex escape strategy. They are led by Squadron Leader Roger Bartlett, nicknamed "Big X," who organizes the various experts into teams tasked with tunneling, forging documents, creating civilian clothes, and gathering the necessary materials to aid their escape.

The prisoners work covertly to dig three tunnels, code-named "Tom," "Dick," and "Hilts," each designed to shuttle the prisoners to freedom. They face numerous challenges including the discovery of one tunnel by the Germans, disposing of the excavated dirt in ingenious ways, and the constant threat of discovery by their ever-vigilant captors. Despite these obstacles, the prisoners persist, driven by a collective yearning for freedom and the knowledge that their escape could also serve to divert German resources during the war effort. Their unity and resourcefulness become the cornerstone of their plan, as they inch closer to the moment of truth when they must put their elaborate scheme into action.