By Brandon Mull
Sent to their grandparents' place for two weeks, Kendra and Seth learn the woods are actually a hidden sanctuary for fairies, satyrs, and much darker things, and one rule Seth can't leave alone nearly gets everyone killed.
Kendra and Seth get dropped at their grandparents' house for two weeks, bracing for nothing but woods and rules. What they find instead is Fablehaven, one of the last secret preserves where magical creatures are kept in check by old treaties. The forest holds fairies, a satyr, a witch, and things a lot worse. One rule matters above the rest: stay out of the woods and don't cross the boundaries. Seth, who has never met a rule he could leave alone, breaks it. Then comes Midsummer Eve, the single night the creatures are loosed from every restraint, and everything he set in motion comes due at once. Now the two of them have to save their grandparents, and themselves, from something they let out.
Some children reach a point where gentle scares stop working and they want the kind with real teeth. This is the book I'd hand them. Mull runs the whole thing on consequence: Seth breaks a rule, something goes wrong, and the danger climbs chapter by chapter toward a genuinely frightening Midsummer night, so you keep reading because you have to know how bad it gets. Kendra and Seth feel like a true brother and sister, one careful and one reckless, and it takes both of their temperaments to get everyone through. The world is deep and rule-bound, the sort a child wants to move into and stay, and four more books follow this one. It's the sturdiest and scariest book on the shelf, which is why it sits at the far end.