For the first time, Percy Jackson enjoys a normal and peaceful life. Everything is changing in the last day of school, when a game of dodgeball seemingly banal turns into a life and death confrontation with a team of giant cannibals. To save his life, Percy starts to Camp demigods, but discovers that the threat looms and the camp. Pin to protect "the city" was poisoned, the magical borders and began to lose strength defense against monsters ready to destroy everything. Worried about the changes in the camp and alarming dreams haunted by his friend disappeared Grover, Annabeth, Percy starts with looking cure savior. But for that heroes will have to face terrible dangers hidden in the Sea Monsters.