The Son of Neptune by Rick Riordan is the second book in the Heroes of Olympus series. This book highlights Percy Jackson and two new characters. Percy Jackson, from the 5 previous books of Riordan’s other series, is now 16, lost his memory, and remembers only of the name Annabeth has wound up at Camp Jupiter. One of the new characters is Hazel Levesque. She is the daughter of Pluto. The other new character is Frank Zhang. Frank is the Son of Mars. These three will embark on a new quest to ‘free death’, or more specifically the god Thanatos.