The Son of Neptune is a 2011 fantasy-adventure novel written by American author Rick Riordan, based on Greek and Roman mythology.

The story follows the adventures of amnesiac Percy Jackson, a demigod son of Neptune, also known as Poseidon, as he meets a camp of Roman demigods and goes to Alaska with his new friends Hazel Levesque and Frank Zhang to free the Greek god of death, Thanatos, and help save the world from Gaea, the earth goddess.

After an initial hardcover printing of three million copies, the book has since been released in paperback as well as an audiobook and e-book and translated into 37 languages.

[5] On May 26, 2011, Riordan released both the cover art and the first chapter for The Son of Neptune confirming that Percy would play a role in the book.

Upon arriving, he is attacked by Gorgons — Stheno and Euryale — and successfully defends a disguised Juno and the camp with the help of the guards on duty.

Frank is revealed to also be a distant descendant of Poseidon and his grandson the Argonaut Periclymenus with shapeshifting powers while Hazel died in the 1940s and was recently resurrected by her half-brother Nico di Angelo.

During the trip, the trio learns that the goddess Gaea is awakening from several millennia of slumber with a plan to destroy the gods and the world along with them.

Dana Henderson of the Seattle Post-Intelligencer called the addition of new characters "refreshing and captivating" and claimed that it would "make the reader to want to keep reading".

[12] The Hutchinson Leader's Kay Johnson wrote that the plot was confusing and the first half was not engaging, but thought Riordan should be given credit for introducing Greek and Roman mythology to a new generation.

[13] Kirkus Reviews was positive about the book, thinking that Riordan had "regained his traction" after "spinning his wheels" in The Lost Hero.