Kendra races to find the information she needs to save Seth in this third novel of the New York Times bestselling sequel series to Fablehaven from author Brandon Mull.

Cursed by the Key of Forgetting, Seth has lost all memory of his past--his relationships, his experiences, and who he really is. Lost and vulnerable, he's the perfect target for the dark unicorn Ronodin, who takes him to the Phantom Isle, the secret gateway to the Under Realm. With Seth not himself, he makes the perfect tool for Ronodin's own dark ends.

Kendra is frantic to find her missing brother, but the quest will take her and her companions, including Warren, Tanu, and Vanessa, far from Wyrmroost to Crescent Lagoon--a recently fallen dragon sanctuary made up of many islands and underwater domains. Its caretaker has regained a foothold on one of the islands. If Kendra and her friends can save that sanctuary, they might uncover the answers they need to rescue Seth.

With each sanctuary the dragons overthrow, Celebrant, the Dragon King, comes closer to the dawn of a new Age of Dragons. With the forces of darkness on the march, can Kendra and her allies gather enough power to win the epic dragon war?