Riordan, R: Percy Jackson and the Olympians, Book Four: Batt

As this fourth installment of the Percy Jackson & the Olympians series unfolds, time is running out as war between the Olympians and the evil Titan lord Kronos draws near. Camp Half-Blood grows more vulnerable as Kronos's army prepares to invade. To stop them, Percy and his demigod friends set out on a quest through the Labyrinth.