User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-184.18.60.162-20130417162518/@comment-4649443-20130518022131

That's because of the year/book confusion. There are five books, but they span four years. Unfortunately, Harry Potter is so famous, everyone thinks that any fantasy/adventure series has a 1:1 ratio with books and years.