Percy Jackson Complete Library, Books 1-5

Percy Jackson learns that he is a half-blood: half-human, half-god. He is taken to a summer camp where kids just like him are safe from monsters that like to attack half-bloods.

At camp, Percy learns that his father is Poseidon, god of the Sea and brother of two other gods, Zeus and Hades. When Zeus's master bolt, which allows him to create lightning whenever he wants, is stolen, he threatens to declare war unless the missing bolt is returned by the summer solstice.