In 100 Cupboards, twelve-year-old Henry visits his aunt and uncle for the summer--and maybe for longer, since his parents have been abducted in South America and may or may not return. But don't worry your head about the parents. Their fate or lack thereof is only incidental and doesn't have anything to do with the plot.
So anyway, Henry goes to live with his aunt and uncle, as well as his three girl cousins, the oldest of which has no personality and almost the same amount of role in the plot as Henry's parents. Henry is given the little attic room and soon discovers 99 little cupboard doors hidden under crumbling plaster on the wall. One of the cupboards opens onto a green, windy world that Henry can smell and hear but can't see; one of the cupboards is a mailbox--and Henry has mail.
With his cousin Henrietta's "help," Henry reluctantly explores the mysteries of the cupboards and discovers long-hidden secrets about himself and his family. I say "help" because Henrietta is as forceful as Henry is wimpy, and she keeps doing stupid things in order to forward the plot. Her younger sister Anastasia is even worse. Anastasia is nine, but she acts much younger. Both the girls are brats that screw stuff up in order to move the plot along. Henry has to react, react, react to their actions.
The book is beautifully written and sets up the magic and the mystery skillfully. I really enjoyed the first third of the book. It reminds me a lot of The Magician's Nephew; it's wonderfully atmospheric. I also loved the relationship between Henry and his Uncle Frank, which was so much better than the rest of the story that I wished it had been the only part of the story.
Unfortunately, as you can guess from what I've written already, I was not happy with the latter part of the book. Solving the mystery of the cupboards requires a lot of exposition from adults, either in the form of Henry reading a journal written by the cousins' grandfather or from lectures by various of Henry's other relations. The climax got confusing and a little disjointed; we see the same scenes from different characters' points of view, get more exposition, and four new characters are introduced in the last few chapters.
The ending left me furious. Turns out this isn't a book, it's a 150-page prologue for the sequel. Every single thing that happens in this book is just set-up for the sequel--seriously, everything. I can't explain why without dropping spoilers, but I can say that nothing is resolved. That's a good way to lose me as a reader for life.