Another school, another monster coming to kill him, another explosion. That’s the story of Percy Jackson’s educational career. This time, the monsters are empousai—Greek vampires with mismatched legs—disguised as cheerleaders. Percy knows there is something off about them, but it takes a mortal girl named Rachel Elizabeth Dare to open his eyes to what they really are. And that makes Rachel unique, because mortals can’t usually see through the Mist, the magical veil that hides the true form of mythical beings.

The empousai corner Percy and Rachel. Percy slashes one back to Tartarus with his trusty sword, Riptide. The other evades his blade, taunting him with hints about a catastrophe that will soon strike Camp Half-Blood. Before Percy can learn more, she explodes in a fiery ball of flame, leaving Rachel and Percy in a smoking crater that was once Goode High School’s band room.

Rachel urges Percy to run, which he does—right into Annabeth, who was coming to meet up with him. Percy and Annabeth race back to Camp Half-Blood to warn Chiron, the camp’s director, of the impending threat.

Chiron has suspected for some time that an attack is coming. He knows <em>where</em> it will come from, too—sort of. Twisting and twining below the earth’s surface is a vast maze of tunnels: the Labyrinth. Created by Daedalus, an ingenious architect, in ancient times, the Labyrinth is a living entity that grows and changes. It is a place where time and distance have no meaning. It hides monsters and traps for unsuspecting travelers. Those who enter usually lose their way . . . and their sanity.

The only way to navigate the ever-changing maze is to follow Ariadne’s string, an ancient spool of thread that once led the Greek hero Theseus to safety. Luke Castellan has been searching for the string. If he finds it, he can lead Kronos and his army through the Labyrinth to anywhere in the Western world . . . including Camp Half-Blood.

Stopping their enemies means a quest to find the string. It’s rumored to be in Daedalus’s workshop . . . and Daedalus’s workshop is somewhere deep inside the Labyrinth. Percy is ready to go, but it’s Annabeth who’s granted the leadership role. She’s studied the Labyrinth for years and while book-learning isn’t the same as string-following, no one at camp is more qualified to take charge of the quest.

Annabeth leads Percy, Grover, and Tyson to a fissure in the rocks by Zeus’s Fist and into the Labyrinth. Once inside, though, the Labyrinth seems to take charge. The network of tunnels brings them to bizarre and dangerous places—a prison cell in Alcatraz, a Texas ranch with meat-eating, massive manure-producing cattle, a game show—before guiding them to a cave where a familiar and terrifying golden sarcophagus sits. But Kronos isn’t inside. Luke is.