After the near-suicide mission to the Norwegian fjord, which had claimed so many lives, morale among what was left of 633 Squadron is at its lowest ebb. Unbearable tension, stupid wrangling among the survivors and problems with replacement recruits are tearing the squadron apart. The new Commander, Ian Moor - young, brilliant and determined - knows that the only thing that will pull it together again is the challenge of another vital mission. The Germans are developing a new anti-aircraft rocket, code name Rhine Maiden, which poses the most deadly threat so far to the Allies' invasion plans. So the top brass decide that 633 Squadron should first flatten the rocket factory on a bombing run, and then make a daring strike on an underground target buried deep in a Bavarian valley - in broad daylight...