Because Dragonwatch, an ancient group of wizards, enchantresses, and dragon slayers, is crumbling, an uprising of dragons threatens to destroy the magical preserves as well as overrun the nonmagical world.

Seth attempts to halt a plague that is turning Fablehaven's beings of light into creatures of darkness, while his sister Kendra and the Knights of the Dawn attempt to retrieve an artifact before the Society of the Evening Star.

The magical preserve Fablehaven provides refuge to numerous mystical species: centaurs, trolls, satyrs, ogres, fairies, minotaurs, brownies, imps, nymphs, and many others. But some beings are too large and powerful to be confined to regular enchanted refuges. These mightiest of creatures dwell inside the dragon sanctuaries.