text: Fictional demigod Percy Jackson -- who is fifteen years old by the end of the book -- tries to stop Luke Castellan and his army from invading Camp Half-Blood by navigating Daedalus 's labyrinth .
simplified: Demigod Percy Jackson , who is almost fifteen years old , tries to stop Luke and his army from invading Camp Half-Blood by navigating Daedalus 's Labyrinth .