The House of Hades is a fantasy-adventure novel written by American author Rick Riordan, based on Greek and Roman mythology. It was published on October 8, 2013, and is the fourth book in The Heroes of Olympus series, preceded by The Mark of Athena and followed by The Blood of Olympus. The story follows the Greek demigods Annabeth Chase, Leo Valdez, Piper McLean, Nico di Angelo, and Percy Jackson; and the Roman demigods Jason Grace, Hazel Levesque, and Frank Zhang on their quest to close the Doors of Death, stop the Giants from raising Gaea, and prevent war between Camp Jupiter and Camp Half-Blood. The novel is narrated in third-person, alternating between the points of view by the seven demigods of the "Prophecy of Seven". The novel received positive reviews from critics for its more-mature themes compared to previous Riordan novels. During the first week of its release, The House of Hades sold about 350,000 copies, reaching the top of the bestseller lists of The New York Times, USA Today, The Globe and Mail and The Wall Street Journal. Source: Wikipedia (en)