How to Fight a Dragon's Fury

How to Betray a Dragon's Hero is the twelfth and final installment of the How to Train Your Dragon books series.

Plot
The book begins with Hiccup lying on the shore of Hero's End, unconscious. The Wodensfang arrives and wakes Hiccup by pouring water on his face. When Hiccup wakes up, however, it turns out he has amnesia, not even recognizing his own name[1].

With the help of the Hogfly Hiccup escapes from a Sandshark and Vampire Spydragon attack on Hero's End, but the Wodensfang is tranquilized and rendered unconscious. He reaches the Island of Tomorrow despite an attack by the rebel dragons with the help of Fishlegs and Camicazi, even though he doesn't yet recognize his friends. The Dragon Guardians of Tomorrow permit him to land on the island even though he doesn't knowingly hold any of the King's Lost Things.

On the island of Tomorrow, Alvin the Treacherous is about to be crowned King. Hiccup challenges Alvin and claims the Kingship for himself. With the intervention of Fishlegs, and the reading of Grimbeard the Ghastly's will, and the help of Nanodragons, the assembled Viking tribes affirm Hiccups claim, and he is crowned king, and he regains his memory.

At this point Wodensfang awakes and asks if Hiccup has found the "real" dragon jewel, explaining that the jewel that Hiccup found in the swallowing sands was a decoy. The real jewel contains two fossilized nanodragons, one of which is carrying a deadly plague (which explains the dragons' fear of the jewel)

Without the real jewel, Hiccup must go to face the Dragon Furious in single combat. Hiccup is overpowered, but realizes at the last moment that the real Dragon Jewel must be hidden in the lobster necklace that Fishlegs had given him. With the jewel revealed by Toothless cracking open the lobster claw, Hiccup is able to begin to negotiate a peace with Furious.

However, Excellinor and Alvin disturb Hiccups negotiations and provoke a total war between humans and Dragons. Nevertheless Hiccup manages even now to negotiate a truce, and Alvin is taken to his death by the Dragon Guardians and his own son, Fishlegs for breaking the terms of single combat.

Excellinor attempts to kill Hiccup with a poisoned Stormblade, but Furious steps in front of her and is struck by the sword before he flicked the witch away to her death with his claw. Even though the blade is not long enough to do damage to the Dragon, he is poisoned and knows he is dying. Furious agrees with Hiccup to a permanent peace and leaves his command to Luna, his second -in-command. After that Luna and the dragon rebellion decide to go into permanent hiding in the Northern oceans, until such time as humans can be trusted to live in peace with dragons, while Toothless and the remaining Dragons decide to stay with Hiccup and the others.

The epilogue shows an elderly Hiccup who had built a new kingdom of harmony on Tomorrow where humans and dragons live in peace, but describing how the dragons which had been common in his youth were now rare sights, and how bards were writing stories which described dragons as mythological.