Grip of the Shadow Plague

Kendra and Seth along with Grandpa and Grandma Sorenson discover that someone or something has released a plague that is turning the light creatures of Fablehaven into creatures of darkness. And for the first time, Kendra and Warren must visit another magical preserve called Lost Mesa in Arizona and try to recover another hidden artifact. Can the plague be stopped? Can the artifact be found? And most importantly, is the Sphinx a traitor?