The case of the pirate U-boat!Air Commodore Raymond has a thrilling new case for Biggles, Ginger, Algy and Bertie, now the Scotland Yard Air Squad.Instead of surrendering at the end of the war, commander Von Schonbeck of submarine U-517 escaped to the south Indian ocean. From his base on an uncharted island, he has been waging his own personal war, very profitably. Among other booty, he is known to have acquired a sizeable quantity of gold.But there's very little to go the submarine sinks all the ships it preys upon, leaving no survivors. And Biggles & Co. have a hunting ground of a million square miles of air and ocean?Will they find the renegade submarine, or will it continue to prowl the depths?Has Biggles met his match in the hunt for the dastardly von Schonbeck?