Drama recounting the Nazis’ efforts to develop the atomic bomb and the Allies’ desperate struggle to prevent it from happening. German scientist Werner Heisenberg is asked to join a secret project to create an atomic bomb at Norsk Hydro’s factory in Norway, but when the Second World War breaks out, professor and army reserve Leif Tronstad is suspicious of the Nazi request for heavy water production. He flees to England to warn of the potential threat.
While the Nazis are working on the first atomic bomb, the saboteur group Grouse is assembled from local resistance members who assist British commando forces in blowing up the heavy water facility. Werner Heisenberg travels to Copenhagen to meet his Danish mentor Professor Niels Bohr, who implores him to stop working on the bomb, but Heisenberg fails to understand his reasoning and dives back into his work.
The British mission fails when both planes crash-land and the surviving soldiers are killed by the Nazis. The Americans insist on bombing the factory, but Leif Tronstad feels this will be futile and persuades the Allies to send in a team of Norwegians, selecting five men for this `Gunnerside’ mission to bomb Vemork.
The most famous of the four sabotage actions in the Heavy Water War sees local saboteurs, trained in England, set out to bomb a water facility outside Rjukan. The team members abandon the original plan to shoot their way across the bridge and into the factory, opting to climb the steep walls of the ravine under the bridge, which are not protected.
Despite being badly wounded, Claus Helberg manages to escape the Germans and return to England. Werner Heisenberg continues his research without heavy water while the factory is rebuilt as Bjorn Henriksen is arrested after refusing to give priority to increasing the delivery of the commodity The Americans learn the Germans are rebuilding the factory, so decide to bomb it against Leif Tronstad’s advice.
The Allies order the remaining members of the Gunnerside team to sink the ferry carrying the heavy water facilities across the lake from Rjukan. When Werner Heisenberg’s superior Kurt Diebner shows him secret documents about the effects of radiation, he is left full of despair. Meanwhile, the explosives are placed below deck on the ferry and, when they detonate, those on board are plunged into the ice-cold water.