Heroes Of Olympus Bk 4 House Of Hades

After 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 prevent the giants from raising Gaea. But how will Percy and Annabeth escape?