I think you are looking for "THE LIGHTNING THIEF: Percy Jackson & the Olympians, Book One"
by Rick Riordan.
The story begins with a warning that everything in this book is purely fictional unless the reader starts to experience stirrings and have feelings like those of the hero. If that happens, then the reader is advised to close the book and stop reading immediately. The hero, 12-year-old Percy Jackson, is far from your ordinary, everyday high school student. In fact, he is about to be kicked out of his third high school.
Try as he might, Percy just cannot behave himself and settle down to study. His mother understands, for reasons unbeknown 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 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). Because of Percy's 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.
As you might imagine, terrible and unusual occurrences happen to Percy and his two friends, with monsters and disaster at every turn. If you can suspend disbelief, you will find this book similar to the old-time movie serials, except that the villains and heroes are Greek mythological figures.
