A group of war prisoners has spilt blood, sweat and tears to construct a bridge over the river Kwai in Thailand. Just when the bridge is ready, an American bomber arrives and destroys it. Camp commander Tanaka wants to set an example and orders that some of the prisoners must be executed. Just in time major Harada arrives with orders that the healthiest prisoners must be transported to Japan by train and boat. A treacherous journey since the allied forces keep a close eye on railroads and practically own the seas. The prisoners are thinking of plans to escape. Meanwhile the American bomber has been shot down and its pilot, Leyland Crawford, is being rescued by the indigenous people, the Meo. The Meo have formed a resistance group against the Japanese, led by the British colonel Grayson.