The Battle of the Labyrinth
Using the Labyrinth, Percy has to try to find Daedalus so Luke cannot get Ariadne's string, thereby foiling Luke's invasion. Ariadne's string is used to find all the exits of the Labyrinth. Grover comes to the rescue and causes a Panic to scare away the enemy. After the battle, Daedalus sacrifices himself to close the labyrinth, which is tied to his life.