Trying to be patient as one of the only kids in her class who has not been chosen by a pet monster, little Marilyn decides to search for her monster even though she is supposed to wait to let a monster choose her.

When demonic cheerleaders invade his high school, Percy Jackson hurries to Camp Half Blood, from whence he and his demigod friends set out on a quest through the Labyrinth. Meanwhile the war between the Olympians and the evil Titan lord Kronos draws near.

The disappearance of the goddess Artemis while out hunting a rare, ancient monster, prompts a group of her followers to join Percy and his friends in an attempt to find and rescue her before the winter solstice, when her influence is needed to sway the Olympian Council regarding the war with the Titans.