Percy Jackson - the young demi-god and son of Poseidon - has had an unnervingly quiet school year. But then during a near-death experience in a dodgeball game on the last day of school, Percy discovers that the magical borders protecting Half Blood Hill, a summer camp in Long Island dedicated to training young demi-gods, are failing. The only way to restore the power of the borders is to find the mythical Golden Fleece, which has been missing for centuries. Percy must undertake a dangerous voyage - to find the fleece AND to save his friend Grover - but if he fails to return by the end of the summer, Camp Half Blood will be destroyed . . .