After a visit from Vandrone, the master he first encountered in Egypt, Nathan prepares for his third and final journey with his housekeeper and one of his students. The unexpected arrival of old friends at Gladwick Hall leaves him little choice but to invite them to join him in his quest for the sorcerer's mask. Nathan books passage on the Barracuda, a unique one-man submarine, captained by a crazy German. The voyage looks to be in peril as the small craft battles on, through treacherous weather and heavy seas, to the most dangerous place on earth - the Island of Two Moons. In hot pursuit, on a ghost ship, are two of his sworn enemies. At the helm is a villainous cutthroat - a demon of revenge who has been summoned from a watery grave.