During World War II, a small band of Norwegian commandos endured months in the frozen wilderness, surviving on moss and reindeer meat, to stop the Nazi nuclear program. This episode tells the story of the heavy water sabotage at the Vemork plant, where the world's first mass production of heavy water threatened to give Germany the moderator it needed to breed plutonium. We explain the physics of why a moderator matters and how a single German oversight with impure graphite pointed their atomic ambitions straight at Norway.

We follow the daring operations: the failed glider assault of Operation Freshman, the cliff-scaling triumph of Operation Gunnerside complete with the surreal search for a caretaker's eyeglasses, the Allied bombing raids, and the agonizing decision to sink the ferry carrying the heavy water, killing innocent civilians. A 2 ...