This book starts with Percy Jackson preparing for his high school orientation. Then a mysterious mortal acquaintance appears. Demon cheerleaders also appear. Percy finds out that time is running out as war between the Olympians and the evil Titan lord Kronos is commencing. The safety of Camp Half Blood is at steak. This is because Kronos's army is preparing to invade the impenetrable borders. Percy and his demigod friends need to set out on a quest through the Labyrinth-a sprawling underground world. There is danger at every turn.