Set in German-occupied Norway, this is an embellished account of the remarkable efforts of the Norwegian resistance to sabotage the German development of the atomic bomb. Resistance fighter Knut Straud enlists the reluctant physicist Rolf Pedersen in an effort to destroy the German heavy water production plant near the village of Rjukan in rural Telemark. In the process, Pedersen discovers that his ex-wife Anna and her uncle have also joined the resistance. British commandos dispatched to destroy the plant are killed when their glider hits the mountainside at night. An improvised raid by the resistance ends in the partial destruction of the heavy water canisters, but the contingency plans of Reichskommissar Terboven enable the Germans to resume production quickly. Pedersen wants to recommend to London that the Allies bomb the plant. Straud opposes him because of the potential death toll on Norwegian civilians and a fight ensues. They send in separate recommendations, and the air raid takes place, but it fails to destroy the heavy water. A Norwegian traitor gives away the resistance hideout, and Anna’s uncle is killed. The Germans load the canisters onto a ferry for shipment to Germany, and the resistance rig explosives to sink the ferry in the fjord. As the ferry is about to leave, it is boarded by the widow and baby of one of Pedersen’s and Straud’s colleagues. Pedersen boards the ferry and organizes a children’s game of “lifejacket” in order to minimize civilian deaths. The film closes with resistance members rescuing passengers as the ferry sinks.