This is book four of the Percy Jackson series, with only one more installment to come. Readers from around ten years old will be thrilled by the adventures of the teenaged hero who just happens to be the son of Poseidon, God of the Sea, and all his friends, most of whom are the children of the Olympians from Greek Mythology.
In my opinion, it would be better if you read the series in order, and the three previous books are:
The Lightning Thief (Percy Jackson and the Olympians, Book 1) The Sea of Monsters (Percy Jackson and the Olympians, Book 2) The Titan's Curse (Percy Jackson and the Olympians, Book 3)
In "The Battle of the Labyrinth", Percy and three friends set off on a quest through the treacherous labyrinth, in search of the inventor Daedalus, hoping that he will help them to defeat the army being assembled by Luke, son of Hermes. The thing is - Luke is just the messenger, and the evil he's about to unleash can bring down Olympus itself.
Although still clueless about girls and relationships, Percy starts developing and unleashing his powers, and surprises even himself when he attempts to repeat Hercules' great stable cleansing project. Other demi-gods also come into their own in book four, and a mortal girl proves to be just the ticket, and in the nick of time too. In a related sub-story, the search for Pan reaches an exhilarating climax.
Packed with monsters of all persuasions, gods and demi-gods, rescues, battles and side trips to Alcatraz and Mount St. Helens, this is by far the most exciting book of the series so far.
Amazingly imaginative, thrilling and funny, this series by Rick Riordan continues to be a front runner in children's fiction, and I recommend it without reservation.