As thirteen-year-old Madison tries to figure out how she died and ended up in Hell, she learns how to manipulate the corrupt system of demons and bodily fluids.

"Now that Nikki Beckett's boyfriend has been sucked into the tunnels of the Everneath, Nikki must journey down to the underworld to bring him back before he is lost forever."--

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 both sides and prevent the giants from raising Gaea....