I have been engulfed in the Percy Jackson series. I can not put the books down! It's a good thing they aren't lengthy because I wouldn't get anything else done.
The Titan's Curse begins with Percy, Annabeth, and Thalia going to help Grover with some new half bloods. While trying to rescue the demigods, dangerous monsters intervene and kidnap Annabeth. In this book, Percy befriends a few Hunters and goes on a quest with his friends to rescue Annabeth and save the world...again.
I guess I can relate these books to the Harry Potter books. They are similar in some ways. They are both about teenagers fighting to save the world, they are both fantasy type books, and they are both highly addictive. If you haven't started reading either series, get off the computer, go to the library, and READ THEM NOW!!