The Battle of the Labyrinth

The Battle of the Labyrinth is a 2008 fantasy-adventure novel based on Greek mythology and the fourth book in the "Percy Jackson &amp; the Olympians" series by Rick Riordan. 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. It was released on May 6, 2008 in the US and Canada.
Synopsis.
Plot summary for the Book.
After being attacked by Empousai cheerleaders at his new school, Percy returns to Camp Half-Blood and learns about "The Labyrinth", part of the palace of King Minos in Crete that, according to Greek mythology, was designed by Daedalus. During a battle game at the camp, Annabeth and Percy find an entrance into the Labyrinth. Percy soon learns that Luke had used the entrance and will lead his army through the Labyrinth straight in to the heart of Camp Half-Blood. To get into the Labyrinth, Percy has to find the Delta Symbol (Δ) on a passageway, touch it, and then enter 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.
Critical reception.
"The Battle of the Labyrinth" received generally positive reviews. "Publishers Weekly" praised Riordan saying, "One of Riordan's strengths is the wry interplay between the real and the surreal." and adding that "The wit, rousing swordplay and breakneck pace will once again keep kids hooked." "Children's Literature" said, "Riordan creates a masterful weaving of Greek mythology and traditional fantasy in this latest book in "The Olympians" series. Fans will enjoy the latest adventures of their favorite characters, and those picking the book up for the first time will have no trouble falling into this magical world." However "School Library Journal" wrote "Like many series, the "Percy Jackson" books are beginning to show the strain of familiarity and repetition." before adding: "However, the overarching story line remains compelling, and the cliff-hanger ending will leave readers breathless in anticipation of the fifth and final volume." "Kirkus" adjudged the book to be the best in the series and said, "The often-philosophical tale zips along with snappy dialogue, humor and thrilling action, culminating in a climactic battle between gods and Titans.
Awards and nominations.
"Kirkus Reviews" gave "The Battle of the Labyrinth" a starred review as well as "Publishers Weekly."
Audiobooks.
"The Battle of the Labyrinth" was adapted to a 10 hours and 32 minutes audiobook read by actor Jesse Bernstein and published by Listening Library. The release date for the audiobook was May 13, 2008.
AudioFile Magazine was generally positive about the audiobook. They commended Bernstein, saying that he was "just as skillful at wringing humor from the witty dialogue and from the contrasts between the modern and ancient worlds." 
Sequel.
In "The Last Olympian" there is a final battle for Olympus, with Percy and his friends defending it against Kronos and his forces. Percy rallies the demigods and many of his allies take part in the war, including The Hunters of Artemis and the Party Ponies. Rachel becomes the new Oracle and spouts another Great Prophecy. Percy and Annabeth start going out.
"The Last Olympian" was released May 5, 2009. It is the last book of the series.