The House of Hades (pdf) is a fantasy-adventure novel written by American author Rick Riordan. It was published on October 8, 2013 and is the fourth book in The Heroes of Olympus series.
With characters based on Roman mythology, while on their quest to close the Doors of Death, Percy Jackson and Annabeth stumble into a pit that leads to the underworld. When Percy and Annabeth realize that they are inside the physical body of Tartarus, the two begin their journey through the terrifying landscape toward their destination, the Doors of Death. Their goal is to close those portals. If they are successful, underworld monsters will be prevented from returning to the mortal world.