Kendra and her brother Seth are sent to stay with their grandparents for a couple weeks while their parents are on a cruise. They don't know Grandma and Grandpa Sorenson very well, in fact, Grandma Sorenson isn't even at the house. Kendra and Seth are given full reign of the house and yard, but are told to stay out of the forest.
Of course, Seth can't help but wonder what's in the forest, and he wanders in one day. Kendra wonders at the giant butterflies and dragonflies in the yard, until she notices their odd behavior. They drink milk--so Seth and Kendra also try it. Turns out, their grandparents are the caretakers of Fablehaven--a sanctuary for mystical and magical creatures. And when Seth accidentally insults the fairies, everything dissolves into chaos. Grandpa Sorenson is kidnapped and it's up to Kendra and Seth to put aside their fears to save him.
The first in the series, there are a lot of things going on here. The point of view shifts a little at the beginning of the book, but the story distracts from that. The whole book is part mystery, part fantasy, and part realistic fiction. Kendra and Seth are well developed and likable. An excellent first book in a series.