During this true-life Second World War story, eccentric inventor Dr. Barnes Wallace (Michael Redgrave) develops a new type of "bouncing bomb" for use in attacks on the dams of Nazi Germany. With help from the Sir David Pye (Stanley Van Beers) at the Ministry of Defense and approval from the government, a special R. A.F. squadron is formed to help develop and use the weapon, culminating in a raid on the dams of the Ruhr River valley.