Rick Riordan - Percy Jackson and az olimposziak 4. - Battle a labirintusban (2011)

Percy Jackson wasn't expecting anything good from the school open day, but when he meets two cheerleader demons after a mysterious mortal acquaintance, things take a turn for the worse.
In the fourth volume of the hit series, the war between the Olympians and the god Titan is on the verge. Even Camp Half-Blood, considered a safe haven until now, proves vulnerable when Kronos and his army try to get within its magical boundaries.
To stop the attack, Percy and his demigod friends go on a mission to the Labyrinth - the vast underground world, which has another blood-curdling surprise in store for them at every turn.