Kendra and Seth Sorenson are the grandchildren of the caretakers of Fablehaven preserve, one of the few places left on earth where magical creatures can live on in an increasingly skeptical world. The trouble is, not all magical creatures are nice. In fact, some of them are downright evil. All the worst ones have been locked away in a magical prison, and if they ever get out, the world as we know it is basically over.

In Book 3, Kendra and Seth are still at Fablehaven with their grandparents. Suspicions have been cast on the Sphinx and his loyalties. Kendra has been recruited as a Knight, and the family agrees that she should infiltrate with hopes of claiming the next artifact before the Sphinx can get to it. And Fablehaven is under attack by a mysterious darkness that is spreading extremely fast.