Fablehaven: Grip of the Shadow Plague (Fablehaven) by Brandon Mull
This is the third book in the fablehaven series and it was every bit as good as the first two. Just like the others it is appropriate for both children and adults. The story was well paced and very interesting. I absolutely loved it and can't wait for the next one to come out!
Description: Kendra and her brother, Seth, have been staying with their grandparents on the magical preserve Fablehaven for the summer. Since the recent revelation that their greatest ally may actually be their most powerful enemy, worry and suspicion have haunted their every move. The secret society seeking to destroy the magical preserves is continuing to move their plans forward. Now, a terrible illness is corrupting the good creatures of Fablehaven. With the help of old friends and new allies, Kendra and Seth must discover the source of this plague before Fablehaven self-destructs.