I am so glad I read this book before giving it to my nine year old due to the "coming of age" theme. It contains several references to nudity and sex between the nephilim (fallen angels) and humans. (This is noted in the Bible as one of the reasons for the flood.) This book is better suited for the teen age group and promotes abstinence/innocence. The twins are not able to ride unicorns if they loose their innocence. One of the boys is regularly tested in this area. It is set in Noah's time period with the twin boys from the previous 3 books at age 15. In the prior books the twins never take part in the action, so it is nice that they get a book on their own. The only drawback is that it was out of place in the time line of the previous books. I loved the biblical tie ins throughout the story with Noah's family. It raises several provoking thoughts about Noah possibly having more children that may not have been let on the Ark (ie a girl Yalith who is taken to heaven like Enoch). Madeline does this by referencing that women were rarely mentioned in the Old Testament. Other children are mentioned that are not allowed on because of their interrelations with the nephilim. Overall, it was a wonderful story with great spiritual content and lessons. It talks of taking out time to be quiet and listen to God talking in the wind. It is a wonderful good versus evil book.