The House of Hades (Heroes of Olympus, Book 4)

At the conclusion of The Mark of Athena, Annabeth and Percy tumble into a pit leading straight to the Underworld. The other five demigods have to put aside their grief and follow Percy's instructions to find the mortal side of the Doors of Death. If they can fight their way through the Gaea's forces, and Percy and Annabeth can survive the House of Hades, then the Seven will be able to seal the Doors from both sides and prevent the giants from raising Gaea. But, Leo wonders, if the Doors are sealed, how will Percy and Annabeth be able to escape? They have no choice. If the demigods don't succeed, Gaea's armies will never die. They have no time. In about a month, the Romans will march on Camp Half-Blood. The stakes are higher than ever in this adventure that dives into the depths of Tartarus.

• The Blood of Olympus (The Heroes of Olympus)
• The Mark of Athena (Heroes of Olympus, Book 3)
• The Son of Neptune (Heroes of Olympus, Book 2)
• The Lost Hero (Heroes of Olympus, Book 1)
• The Blood Of Olympus (The Heroes of Olympus)
• The Mark of Athena (Heroes of Olympus, Bk 3) (The Heroes of Olympus)
• The Red Pyramid (The Kane Chronicles, Book 1)
• The Serpent's Shadow (The Kane Chronicles, Book 3)
• The Throne of Fire (The Kane Chronicles, Book 2)
• The Heroes of Olympus, Book Five The Blood of Olympus