The film contains fine performances from several well-known British comedy and character actors, including James Robertson Justice, Stanley Baxter as both a dour Scottish prisoner and the camp Kommandant, Eric Sykes as a sports fanatic, John Le Mesurier as the Escape officer, Leslie Phillips, and Richard Wattis as the emotional Entertainments officer, desperately trying to coax quality performances out of would-be entertainers.
Sir Earnest Pease (James Robertson Justice) is a brilliant but acerbic scientist working on aircraft research during World War II. He needs to takes a trip on a bomber to observe the results of his work. At first the plan is to fly in an RAF plane but when he is told to shave off his beard he refuses and gets to go in a Royal Navy bomber where beards are allowed.
Because it is vital that nobody knows who he is, Pease goes on the trip as Lieutenant Farrow, a public relations officer.
The bomber is damaged over Germany and he is sucked out of a hole in the side of the airplane but lands safely with the aid of a parachute. He is captured and, after interrogation under his alias of Lieutenant Farrow of the Royal Navy, he is sent to a POW camp, mostly occupied by RAF officers.
His excellent command of the German language causes him to be suspected of being a German agent, but when his real identity and importance becomes known to the Senior British Officer (Norman Bird), orders are given that the men in his hut cooperate to help him escape.
Pease initially views his somewhat happy-go-lucky fellow prisoners, especially Jimmy Cooper (Leslie Phillips), Everett (Stanley Baxter) and "Bonzo" Baines (Jeremy Lloyd) with disdain, but comes to understand and appreciate their optimistic attitudes under the prison system they find themselves in, even if he remains as pompous and arrogant as ever.
Pease/Farrow concocts a plan whereby he is believed to have escaped "through the wire". In fact, he plans to go into hiding and later walk out of the camp, disguised as one of three visiting Swiss Red Cross observers. Crucial to the escape plan is that the scotsman (Baxter) looks exactly like the camp Commandant (even though he describes him as "hideously ugly"). He must pretend to be the Commandant if Pease/Farrow is to escape.
Whilst the prisoners busy themselves with organising camp concerts and sports, the plan goes ahead. But it nearly comes unstuck at the last moment, when one of the prisoners, "Grassy" Green (John Forrest) is revealed as a real Luftwaffe officer and spy. He is "dealt with", and Pease, Cooper and Baines calmly walk out of the camp and eventually make their way back home.
The escape plan, to walk out of the camp dressed as Red Cross observers, actually happened. It was briefly mentioned in Paul Brickhill's book The Great Escape.
The story is told in flashback when, long after the war, Pease is the subject of a TV show based on This Is Your Life during which he is re-united with the other ex-POWs and even gets to meet the former Commandant, who now runs a holiday camp.
"Cooking requires no intelligence. Were it otherwise women would be no good at it."