During the second world war, Nobel price winner Werner Heisenberg is the head of the nazis atomic project. Heisenberg needs heavy water for the reactor he is building, only produced by Norwegian Hydro at Vemork. The creator of the heavy water factory, scientist and resistance fighter Leif Tronstad, come to be sucpicious of the german purchase of heavy water and contacts English intelligence.

The English mission fails and the allies now wants to bomb the heavy water plant. Leif Tronstad persuades them to submit a Norwegian special force group to blow up the factory. Tronstad collect saboteurs, name the group Gunnerside and start training.