Dragonheart: Battle for the Heartfire

Gareth and Rhonu had a son named Walter years after becoming rulers. After Gareth spent most of his time helping Drago, and Rhonu died after her bonded dragon's death, Walter became disillusioned with dragons and ran away. Years later, Walter's wife gives birth to fraternal twins with strange patches of scales on their bodies and dies; Walter raises them despite their appearances.

Twenty years later, King Gareth nears death, and succession is in doubt with Walter still missing. Gareth passes, but Drago survives, learning he is now bonded to someone else. Drago finds his heart now bound to Edric, the male twin who possesses enhanced strength and uses it as a sheriff for Earl Robert Cole's shire. Learning that Walter was Edric's father, Drago convinces Edric to take Gareth's throne in Lundenwic; despite the people loving Edric, his arrogance and inexperience with royal duties bother Drago. Realising their bond is partial, Drago confronts Edric, who shares his twin sister Mehgan's existence. Mehgan grew up prejudiced because of her more visible scales and power to manipulate fire. After she accidentally burnt down their home with Walter inside, Edric bargained to send her away by boat to protect her from the villagers. Unwilling to forsake the chance to be Robert's sheriff, he did not go with Mehgan.

Edric later learns that Vikings have invaded, and he rides out with his army to meet them. Still refusing to trust Drago, he ignores advice to let Drago fight and instead challenges the Norsemen's leader to a duel, only to find that it is Mehgan. The twins have a meeting where Drago teaches them about the Heartfire, the source of his fire breath. Mehgan demands the throne as she is the firstborn twin, but Edric refuses and ends the negotiations. Mehgan and her army sneak into the camp overnight, and she drains the Heartfire from Drago while he sleeps. The Norsemen start their attack, and Mehgan reveals her control of the Heartfire. Overwhelmed by Mehgan's power, Edric surrenders. Once Mehgan and the Vikings secure control, she banishes Edric, unaware that Thorgrim sent men after him. Edric flees to Robert's shire and requests aid in opposing Mehgan, but Robert betrays him to the Vikings, who take him aboard a boat to sell him into slavery. While Mehgan improves women's rights in the kingdom, she tells a captive Drago what happened after Edric sent her away. After emerging as the sole survivor of a storm, she drifted until running aground in Daneland, where her powers caught Thorgrim's attention. Edric tries escaping his captors but nearly sinks the boat. After locals free him from captivity, Drago rescues Edric, and they later receive aid from a theatre troupe. They reconcile as Edric reveals his guilt over his hateful last words to his father and sends Mehgan away alone. Edric learns Drago is dying without the Heartfire, so they sneak into the castle with the troupe's help. When Edric attempts to take the Heartfire from Mehgan, he sees Thorgrim's right-hand woman, Sable, trying to kill her. Edric's warning saves Mehgan, but their refusal to cooperate allows Sable to give Thorgrim the Heartfire, and he promptly targets the twins.

Drago saves the twins from getting captured and forces them to fight to the death for the throne; they fight and argue until Mehgan reveals what really happened when Walter died: Edric accidentally killed their father during a fight over him becoming sheriff, and she took the blame to protect his chance at a good life; the truth compels them to reconcile. Returning to the castle, Edric challenges Thorgrim to get the Heartfire, while Mehgan rallies the castle's women to help her fight. Mehgan finds an open flame, but Sable and an archer mortally wound her, also affecting Drago. Thorgrim absorbs the Heartfire to control its power but gets overwhelmed. Edric kills him, scaring off the Vikings, and Mehgan recovers the remaining Heartfire. Instead of taking it back, Drago has Edric use it to heal Mehgan. Then the twins share the bond of their dragonhearts, removing their scales and powers. With Gareth's family whole again, Drago dies peacefully and becomes a new star in the Draco constellation's tail, telling the twins to rule their kingdom together.