"The Son of Neptune" is the second book in Rick Riordan's "Heroes of Olympus" series, continuing the adventures of demigods in a modern setting. The main character, Percy Jackson, who has lost his memory, arrives at Camp Jupiter, a training ground for Roman demigods. He is joined by Hazel Levesque, a skilled warrior with a mysterious past, and Frank Zhang, who possesses unique abilities linked to his ancestry. Together, they must work together to fulfill a prophecy and free the god of death, Thanatos, who has been captured.
The trio embarks on a perilous quest to the land of the Gaea’s forces, facing various monsters and challenges that test their strength, bravery, and friendship. Along the way, they uncover deeper truths about their identities and destinies. Percy struggles with his lost memories while forming strong bonds with Hazel and Frank, who both have their own personal struggles with their lineage and fate.