Norway, December 1942. Following the German occupation of the power plant at Vemork in southern Norway, the British government has become aware that Hitler is trying to find a way to use the heavy water it produces to make a nuclear weapon. One mission to destroy the power plant has already failed and time is running out. Now the Allies' fate rests in the hands of four teenagers - Jakob, Freddie, Ase and Lars - who must survive for weeks in the freezing conditions of the Hardanger Plateau before they launch a sabotage attempt that will decide the course of the war.