1943. Stalag Luft III, a Prisoner of War camp deep within Nazi Germany. Alllied prisoners eye their captors with uneasy resignation. The prisoners know it is every POW's duty to escape, but security at the camp is high. After watching prisoners playing leap-frog, Peter and John hatch an ingenious plan to use an exercise yard vaulting horse to cover the construction of an escape tunnel.
Despite initial concern from other officers forming the 'escape committee', they construct a large wooden vaulting horse, advertising it as 'maintaining morale' through exercise. Each day either Peter or John are hidden inside the horse and taken with it into the camp yard, where they dig their way under the fence, the noise of their tunnelling covered by the noise of their fellow prisoners exercising. At the end of each day they cover the tunnel entrance, return to the horse and are carried back to their huts.
After months of digging, both the tunnellers and their accomplices above are growing weak. After a tunnel collapse that is hastily covered by the vaulters, and in which Peter narrowly escapes detection, Peter and John realise they have to change approach. In an effort to increase the pace, they invite Phil (David Tomlinson) to join them, by organising the vaulting while they both descend into the tunnel.
German 'ferrets' (guards) search the hut where the tunnellers are hiding their excavated soil, but their attention is distracted when another group of guards discover a different tunnel. This prompts another increase in pace, not only in the tunnelling, but also in the preparation of maps, German money, fake clothes, identity papers, and passports.
As the vaulting horse can only carry two at one time, John agrees to be sealed into the tunnel to wait for Peter and Phil to join him. The Camp's senior British officer stands in for John at roll-call to help the trio avoid early detection. The others join John and wait for nightfall. At an agreed time the Camp goes into a frenzy of noise - shouting, tins banging, stamping of feet - and the German guards are suitably distracted from Peter, John and Phil emerging from their tunnel outside the 'wire'. As agreed, Phil heads off on his own, and Peter and John disappear into the darkness together.
Peter and John head for the railway station, where Peter's lack of foreign language skills leave him skulking in the background, as John orders tickets, both travelling as immigrant workers to a port town. Their escape is nearly foiled when one of the principal 'ferrets' disembarks from a train and walks past them. Not noticing them out of the Camp context, he departs and they jump onto their train as it leaves the platform.
With the escapees successfully on their way, the Camp Kommandant parades the remaining prisoners, listing the loss of privileges forming their punishment. He is met with jeers, which turn to cheers as the wooden horse is carried away from its storeroom by the German guards.
Peter and John make their way to Lübeck, climbing into the docks in an attempt to contact Swedish seamen who may aid their escape. They are discovered and chased by German soldiers, narrowly avoiding capture, and similarly evade detection by a policeman when back in the town. They decide to check into a hotel, and then make contact with a group of French Workers, who agree to assist them.
A Danish resistance worker smuggles them by boat to Copenhagen to stay temporarily with his sister. When he returns with the news that the occupying Germans and the local police are looking for them, he leads them to a small fishing village. Detected by a German soldier, Peter is reluctantly forced to kill him or face re-capture. They are then taken onto a small boat and cross the sea to neutral Sweden.
Safe on neutral territory in a plush hotel restaurant, Peter and John are overjoyed to meet Phil (who has also managed to avoid re-capture) and they adapt uneasily to the luxury around them, far from the hardships of Stalag Luft III and their escape.
