Dragonwatch 4 is the fourth book in the Dragonwatch series by Brandon Mull. It follows the adventures of Kendra and Seth Sorenson and their dragon allies, as they battle an ancient evil that threatens to destroy the mythical sanctuary that protects magical creatures.
The story commences with Kendra and Seth discovering an invisible fortress belonging to the mysterious Cult of the Dragon. This fortress houses a powerful type of dragon, known as a leviathan. The dragons had been imprisoned and enslaved by the cult for centuries, used for their destructive power.
Meanwhile, the Fairy Queen has been captured and taken to the hidden fortress. Kendra and Seth enlist the help of their dragon friends and other mythical creatures to help rescue the Fairy Queen and release the dragons from the cult's control. Along the way, they discover the Cult of the Dragon's plans to concentrate the power of the leviathans and use it as a weapon of destruction.
Kendra and Seth must find a way to save the Fairy Queen, free the dragons, and somehow stop the cult. Will they be able to achieve their tasks in time and save the sanctuary? It is up to Kendra and Seth to find out.