The+Lightning+Thief

Try as he may, Percy just cannot behave himself and settle down to study. His mother understands, for reasons unbeknownst to Percy. After beating up a bully who is attacking his best friend, Grover, strange things start happening to Percy.

In fact, after only one or two chapters, Percy's math teacher turns into a horrible, terrifying monster who tries to kill Percy. Then a gigantic Minotour (yes, a Minotour from Greek mythology) chases Percy until Percy tears off one of his horns and he dissolves into sand. Then, a few seconds later, Percy's own mother disappears before his very eyes in a cloud of golden haze.

What is going on? Grover leads Percy into Camp Half-Blood, which, as it turns out, is inhabited by creatures straight out of ancient Greek mythology --- only all this is happening right now, in the 21st century! And Camp Half-Blood is where students like Percy, who discover they are really demigods, are trained in the ways of the Greek gods (shades of Hogwarts School).

Because of Percy's outstanding clever behavior at the camp/school, he is awarded a quest. Someone has stolen the god Zeus's most precious symbol of power: his lightning bolt. Percy's mission, should he decide to accept it, is to find the thief and return the powerful lightning bolt to Zeus before a war breaks out between Olympus and the Underworld.