The Battle of the Labyrinth by Rick Riordan

Percy, Annabeth, Grover and Tyson enter the labyrinth in search of Daedalus. Half-blood Percy discovers more of his powers while Grover and Tyson branch off in search of Pan. Good and evil, heroes versus monsters, struggle with each other midst the fantasy world of magical mythological creatures. Another good adventure in this series. Sandy Penton