Rick Riordan: Percy Jackson and the Battle of the Labyrinth (Book 4): Rick Riordan

After blowing up yet another school, Percy is forced to flee to Camp Half Blood, where he finds all is not well. A dangerous enemy, intent on destroying the secret training camp for young demi-gods, has found a way in through an ancient labyrinth. Percy and his friends must unravel the mysteries of the maze to stop this attack.