Isle of Fire
 Declan Ross, accepting the British offer of pardons to pirates who would turn from their illegal trade, is now attempting to convince other pirates to do the same. Meanwhile, rumors have arisen that Bartholomew Thorne, formerly thought to have been killed in a flood, is alive and plotting. Cat, who has been staying with a group of monks for a time, has been offered the task of commanding a ship full of fighting monks on a mission to hunt down the elusive Merchant. He accepts, and with Ross's permission, takes Anne on as quartermaster. While Ross combs the sea for news of Thorne, Cat and Anne discover the Merchant's underwater lair. Eventually they are separated from their comrades and, in the ensuing battle with the Merchant himself, Anne escapes the lair while Cat is captured. Anne is picked up by the Robert Bruce and Cat, trapped in a cell on the Merchant's ship, is faced with a choice: become the evil man's apprentice or die. The Merchant arranges a meeting with Thorne himself and offers to return Cat to his father for a price. Bartholomew, however, hatefully refuses. Meanwhile, Lady Dolphin, Commodore Blake, and their young friend Hopper sail to an island where Thorne was reportedly last seen. There the two adults are captured by the Raukar, Viking descendants who are under Thorne's leadership. Hopper is able to rescue Blake but Lady Dolphin remains prisoner. While in Bartholomew's captivity, he and she discover that Dolphin is Thorne's daughter, the child of Heather, the wife he lost in a fire. This news confounds the terrible pirate, who, while not fond of Dolphin, now can not seem stay away from her. With a Viking army Thorne sails to London and bombs it with a destructive and mysterious weapon of the Raukar: fire rain. With vengeful satisfaction Bartholomew wipes out and cripples the British Navy and watches the British city in burning confusion. He then sails off to personally destroy the monastery Cat formerly stayed at. Ross and Anne sail to defend the monastery as soon as they learn of Thorne's terrible work. There before the monks' home they confront Bartholomew in a sea battle, which further intensifies with the arrival of the Merchant's ship and a hurricane. In the ensuing fight, Cat boldly escapes the Merchant's ship, that same vessel is sunk soon sunk, Hopper and some of Ross's crewmen rescue Dolphin, and several Raukar ships are destroyed in the hurricane. In a final confrontation on the Ross's ship, Declan, Cat and Stede together kill Thorne. The battered Robert Bruce and its crew ride out the rest of the hurricane in its eye, and then return in triumph to the monastery. As the story ends, London is struggling to recover and rebuild itself and Cat comes to Declan with A question.