After a summer spent trying to prevent a catastrophic war among the Greek gods, Percy Jackson is finding seventh grade unnervingly quiet. His biggest problem is dealing with his new friend, Tyson, a six-foot-three, mentally challenged homeless kid who follows Percy everywhere. But things don't stay quiet for long. Percy soon discovers that there is trouble at Camp Half-Blood: the magical borders that protect Half-Blood Hill have been poisoned, and the only safe haven for the demigods is on the verge of being overrun by monsters.