The Mark of Athena (Heroes of Olympus, Book 3)

In The Son of Neptune, Percy, Hazel, and Frank met in Camp Jupiter, the Roman equivalent of Camp Halfblood, and traveled to the land beyond the gods to complete a dangerous quest. The third book in the Heroes of Olympus series will unite them with Jason, Piper, and Leo. But they number only six--who will complete the Prophecy of Seven?
The Greek and Roman demigods will have to cooperate in order to defeat the giants released by the Earth Mother, Gaea. Then they will have to sail together to the ancient land to find the Doors of Death. What exactly are the Doors of Death? Much of the prophecy remains a mystery. . . .With old friends and new friends joining forces, a marvelous ship, fearsome foes, and an exotic setting, The Mark of Athena promises to be another unforgettable adventure by master storyteller Rick Riordan.

• The Son of Neptune (Heroes of Olympus, Book 2)
• The House Of Hades (The Heroes of Olympus)
• The Blood Of Olympus (The Heroes of Olympus)
• The Lost Hero (Heroes of Olympus, Book 1)
• The Serpent's Shadow (The Kane Chronicles, Book 3)
• The Red Pyramid (The Kane Chronicles, Book 1)
• The Last Olympian (Percy Jackson and the Olympians, Book 5)
• The Battle of the Labyrinth (Percy Jackson and the Olympians, Book 4)
• The Trials of Apollo, Book 1: The Hidden Oracle
• The Throne of Fire (The Kane Chronicles, Book 2)