The story of Son of Neptune book is second part of the series – The Heroes of Olympus by Rick Riordan. The 5 Books Collection Set are Lost Hero, Son of Neptune, Mark of Athena and House of Hades.
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.