High Quality Content by WIKIPEDIA articles! The Son of Neptune is the second book in the The Heroes of Olympus series written by Rick Riordan. The story follows the adventures of an amnesiac Percy Jackson, a demigod son of 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.