What dangers are locked behind the cupboard doors?

Henry isn't brave, but when he hears a thumping and scratching on the other side of his bedroom wall, he can't ignore it. He scrapes off the plaster and discovers mysterious doors -- cupboards of all different sizes and shapes. Through one he sees a glowing room and a man strolling back and forth. Through another he sees only darkness and feels the cold sense that something isn't right. When his cousin Henrietta boldly travels into the worlds beyond the cupboards, it's up to Henry to follow her.

Now that he's opened the doors, can he keep the evil inside from coming through?