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During World War II, Norwegian underground leader Erik Bergman informs the British of the location of a German V2 fuel manufacturing plant.  Situated beneath an overhanging cliff at the end of an easily defended fjord, the factory can be destroyed only by collapsing the cliff on top of it, using light Mosquito aircraft.

Wing Commander Roy Grant's 633 squadron is assigned the task, and Bergman plans a ground attack to coincide with the air strike, but he is captured and tortured by the Gestapo.  Gestapo headquarters is destroyed by the 633 squadron, and Bergman is killed, but not before he reveals the plans for the attack.  Underground resistance is destroyed, and Mosquito pilots, unaware that the ground attack will not take place, fly to the factory, and the entire squadron is wiped out.  However, the last bomb dropped makes the mission a success.  Only Grant and his navigator survive.