The Lightning Thief by Rick Riordan
When things go terribly wrong for Percy at yet another boarding school, his mother realizes it is finally time for Percy to learn the truth about his father’s identity and to go to the only place where he will be safe: Camp Half Blood.
Percy is the son of Poseidon, the Greek God of the Sea. The Greek myths about gods, demigods and monsters are true, and Percy is soon in the thick of an epic quest to reach the gates of the underworld and recover the stolen lightning bolt. Along the way he hopes to rescue his mother from the grasp of death and prevent a catastrophic war between the gods. Adventure and excitement await.