Fablehaven

Fablehaven is governed by ancient treaties that keep its creatures in their place, and those treaties have loopholes. On the night of Midsummer Eve, when the rules weaken, Seth's mistakes unleash forces that threaten the whole family. A strange old woman bound in knots in a shack covered with ivy, a housekeeper with a mysterious past and an imprisoned monster beneath the woods all play their part. Kendra, the cautious one, must eventually do something far braver than she believed possible.

Mull's great strength is world-building with consequences. Every creature has its nature, every rule has a reason, and Seth's impulsive curiosity has real costs. The relationship between the siblings, irritated but loyal, rings true, and the climax is genuinely thrilling. The book also has a satisfying moral backbone without preaching: courage and humility matter, and so does listening to people who know more than you.

The opening chapters move more slowly than the rest, and some younger readers may find a few creatures frightening. But once the story takes off it is very hard to put down. About 384 pages in the Aladdin paperback.