Adopted Into Fablehaven Book 3: The Shadow Plague

While Drake deals with a deep betrayal, Starla's beloved home is under attack. Creatures of light are being transformed into creatures of darkness -- and Starla's family and friends are, too.
But instead of helping Fablehaven defeat the curse, she and Kendra are sent away to retrieve another key to the Zzyzx prison.
(Meanwhile, the Loki Twins cause chaos.)