Heroes of Olympus: The House of Hades (Book 4)
House of Hades (Heroes of Olympus), available in paperback, is the fourth book of the famous The Heroes of Olympus series. It describes the adventure experienced by the seven Olympus heroes, also called the demigods, while they try to fight against evil.
The demigods possess special powers and are the children of Gods and mortals. The series recounts the different quests taken forward by these seven heroes to keep Gaea away from earth. Gaea is the negative character in the book. The third book of this series ends with Percy and Annabeth, two demigods, falling into the underworld prison. It's called Tartarus and is heavily guarded by the Doors of Death.
This book, House of Hades, begins by describing the tough journey faced by Percy and Annabeth as they struggle their way to the Doors of Death. They encounter scary and powerful demons and monsters on their way. At the same time, the remaining five demigods in the mortal world are on a quest of their own to find Percy and Annabeth.
House of Hades (Heroes of Olympus) was published on 15th October, 2013. The book further narrates the events that take place with the scare of the impending rise of Gaea. Danger looms over the mortals on earth and the only way to save them is for the demigods to unite. This requires them to close the Door of Death and Percy and Annabeth are expected to escape before this happens. If not, they would remain in Tartarus forever.