The Question and Answer section for The Lightning Thief is a great resource to ask questions, find answers, and discuss the novel.
From the text:
I'm not sure when I first realized something was wrong.
Probably, it was when I noticed the guy standing next to me at VR sharpshooters. He was about thirteen, I guess, but his clothes were weird. I thought he was some Elvis...
Are you giving me a choice of words or just a general word to think of?
Basically you have to come up with an argument about the book. Your thesis should reflect something you are trying to prove.