Algy and Bertie have brought in the plane, loaded with enough bombs to blow the submarine to pieces, but they cannot use them until they find out what has happened to Biggles. Ginger is sent to search for him and to tell him the good news about the plane. Biggles is in a desperate situation. He and Tom stoutly defend their cave hideout against the attack by Von Stahlein, but the wily German finally defeats them...