Percy Jackson & the Olympians

My 11-year-old son's favorite book at the moment is "The Titan's Curse" by Rick
Riordan.

It is the 3rd book in a series of books by Rick Riordan. My son Ian said that
they are the best books that he has ever read.

From Wikipedia:
"Percy Jackson & the Olympians is a series of fictional adventure and fantasy
books authored by Rick Riordan. Set in the United States, the books are
predominantly based on Greek mythology. The series consists of five books.
The protagonist is Percy Jackson, who discovers that he is the son of Poseidon,
god of the sea and earthquakes. He learns that the legendary beings of Greek
mythology still exist and have always existed, including monsters, cyclopes,
empousae, Titans, and the Greek Gods (Olympians) themselves who dwell in
Olympus, which is now situated at the mythical 600th floor of the Empire State
Building. Percy is frequently attacked by monsters because he is a child of one
of the "Big Three": the lord of the sky, Zeus, the king of the sea, Poseidon,
and the leader of the Underworld, Hades, who made a pact after World War II to
not have any more children because they were too powerful and unpredictable.
Percy meets many other young demigods, both friendly and hostile, who are also
in the process of discovering their ancestry and powers."

1. The Lightning Thief
2. The Sea of Monsters
3. The Titan's Curse
4. The Battle of the Labyrinth
5. The Last Olympian