Christina isn't allowed outside. Her scientist father says it's for her protection, but from what? An orphan boy, a secret tunnel, and a mysterious miniature airplane lead Christina to some shocking truths, including the mystery of her mother's death. Once she finds out that nothing is as it seems, it's suddenly up to Christina to make it all right. Part mystery, part comedy, part science fiction, and a whole lot of adventure, this book is a surefire hit. (Henry Holt and Co., $11.55)