Set in German-occupied Norway, this is based on the efforts of the Norwegian resistance to sabotage 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 in rural Telemark. British commandos dispatched to destroy the plant are killed when their glider crashes. A resistance raid ends in the partial destruction of the heavy water but the Germans resume production quickly. Pedersen recommends that the Allies bomb the plant. Straud opposes him to prevent civilian deaths. The air raid takes place, but it fails to destroy the heavy water. The remaining heavy water is loaded onto a ferry for Germany, and the resistance attempt to blow it up. Pedersen boards the ferry to try and minimize civilian deaths. The film closes with resistance members rescuing passengers as the ferry sinks.