I started this series recently, and I started with the second book in the series. I don't think it makes much of a difference where you start in the series because they are all different stories. They interconnect with how they are each on an adventure (through their grandfather's will) but aside from that each book in the series seems to be a book unto itself. Meaning, if you like one type of book better than another you might have more options in this series because they are not all completely the same. In fact each of the seven books in the series is written by a different author.
Overall, the book was alright. It is a very quick read and can easily be entertaining for boys and girls. There is adventure and mystery involved. However, the mystery is more of a personal goal for the young boy in the novel than a true mystery. Not all of the questions have answers, and that can be frustrating to some readers. So, if you need all the answers at the end of the book I wouldn't necessarily recommend this book. There is a sense of adventure in this book, and it has great historical content, so if as a reader you are interested in history and especially Spanish history I would give this book a try. Like I stated earlier, it is a very quick book to get through, which makes it both good and bad. Good because it's a quick read if you aren't an avid reader and bad because it doesn't completely suck the reader into the story. It could be a better book, but I wouldn't dismiss it if you want something quick and light to read.