The Son of Neptune

The Son of Neptune is the second book in the Heroes of Olympus series, set to be released in November 2011, and was revealed on page 557 of the First American Edition Hardback copy of The Lost Hero.

"The Son of Neptune", (Roman equivalent of Poseidon) most likely refers to Percy Jackson, the main protagonist of the Percy Jackson and the Olympians series. It could also possibly refer to another Roman son of Poseidon, but this is very unlikely, since Percy had disappeared about the same time of Jason. And that both Jason Grace and Percy Jackson are their Camp's Leaders.