The Son of Neptune

Percy has lost his memory and roughly eight months of his life, recalling only a single name, Annabeth; the goddess Juno (appearing as the old woman June) has swapped him with the Roman camp as part of a plan to unite the Greek and Roman demigods. He regains his memories upon crossing into Camp Jupiter.

Percy, Hazel, and Frank travel to Alaska to free Thanatos, the god of death, who has been chained so that souls no longer stay dead; they have only four days before the giant Polybotes and his army attack Camp Jupiter.

Hazel is a daughter of Pluto who originally died in 1942 and was recently brought back from the dead, while Frank is a son of Mars who can shapeshift into animals; both are Camp Jupiter demigods who join Percy's quest.

The book is told in third-person limited point of view that rotates among Percy, Hazel, and Frank, with each character taking blocks of chapters before the perspective shifts, always in the same order.

Camp Jupiter is the hidden training ground for Roman demigods, located near modern-day San Francisco, organized into a legion and led by praetors such as Reyna; it is the Roman counterpart to the Greek Camp Half-Blood.

Beyond freeing Death, the heroes' larger task is to unite the Greek and Roman camps so the Prophecy of Seven can be fulfilled against the earth goddess Gaea; the book is the second of five and is followed by The Mark of Athena.

It is book 2 of the five-book Heroes of Olympus series, following The Lost Hero (2010) and preceding The Mark of Athena (2012); the series itself is a sequel to Percy Jackson and the Olympians.

It was published October 4, 2011, by Disney-Hyperion and is written for a middle-grade audience, blending Roman mythology, adventure, and humor in the same style as the Percy Jackson books.