According to the story on the lightening thief book, Percy is being pursued by Zeus, one of the gods.
<em>This is as a result of the fact that he represent the broken promise made among the gods (that non of them should give birth to a child which posidon broke) and also coupled with the fact that Zeus's master lightning bolt has recently been stolen which made him the prime suspect as a thief.</em>
He has no other option that to search for it and return it before their will be an all out fight between the gods.
