In May 1943, RAF 617 Squadron flew low over Germany at night to breach the Moehne, Eder, and Sorpe dams with a bomb designed to skip across water like a stone. Actor and pilot Martin Shaw retraces the raid's route by air, using his own flying background to test how the pilots managed the altitude and speed the mission demanded. He works through the 1955 film The Dam Busters scene by scene, checking its version against records and eyewitness accounts to sort dramatization from fact. Shaw interviews the last surviving RAF veteran of the operation and a German survivor of the flood that followed the Moehne dam's collapse, along with the wartime girlfriend of pilot Guy Gibson, whose account has stayed largely untold. Aerial footage over the actual dams and river valleys shows the terrain the crews had to navigate in the dark at low altitude. The film builds toward a clearer picture of what the raid actually cost, on both sides of the water.