My son is seven. He devoured the Harry Potter books, but I had him stop after book five. At that point, I was in a real quandry. I needed a book series that would have an age appropriate story line yet challenge him with vocabulary and reading comprehension without being too taxing. The Secret Series was the perfect solution for my young voracious reader.This book will appeal to both boys and girls as there are two main characters of each gender. Plus, the girl isn't overly "girly", so she doesn't turn my son off.The entire series of books has mystery, intrigue, and loads of humor. However, I do recommend starting with book one and reading the subsequent books sequentially.