House of Hades (book 4 of Heroes of Olympus)

Fourth book in the Heroes of Olympus Series. Percy and Annabeth have to meet the other five (and Nico) from the prophecy on the other side of the Door's of Death in order to close them. The future of the world all depends on this and being cast into Tartarus prooves difficult along with the journey to Greece.

(I know the cover says Rick Riordan, but that is because it's the official cover BUT this is my own fanfiction, thanks)