It's WWII and Captain Douglas is a BP executive (Michael Caine) handling incoming fuels for the British Army in North Africa. It is comfortable life until a LRDG colonel (Nigel Green) is told he must put an officer in charge of a dangerous 'Dirty-Dozen mission' to destroy an Afrika Korps fuel depot 400 miles behind enemy lines.
Douglas, who is a fuels expert, is chosen to lead the group despite protesting that he is only a port contractor with an honorary commission. Brigadier Blore (Harry Andrews) dismisses his pleas noting that the executive is wearing a British officer's uniform and is therefore subject to military orders.
Later Captain Leech (Nigel Davenport), the actual mission leader, tells the colonel he doesn't need or want Douglas. But the colonel reminds Leech that as a former officer, who has been recently imprisoned, he has no choice. Nevertheless he is promised an extra 2,000 if Douglas comes back alive.
Disguised as Italian soldiers, the team trek and battle across Rommel's Africa towards the fuel depot.
The film's infamous ending is indicative of the movie's cynical and anti-war attitude.