The House of Hades

The House of Hades, the fourth novel by Rick Riordan in the Heroes of Olympus series, was released on October 8, 2013.
At the conclusion of the previous book in the series, The Mark of Athena, Annabeth Chase and Percy Jackson fell into a pit leading to Tartarus. The protagonists are on a quest to close the Doors of Death, rescue Annabeth and Percy from Tartarus, and stop the Roman demigods from Camp Jupiter from attacking Camp Half-Blood.
The third-person narrators of this book are Percy Jackson, Annabeth Chase, Hazel Levesque, Leo Valdez, Frank Zhang, Jason Grace, and Piper McLean.
Plot
The five remaining demigods: Jason Grace, Piper McLean, Leo Valdez, Frank Zhang, and Hazel Levesque, accompanied by Nico di Angelo and Coach Hedge, continue to set sail towards Greece aboard the flying warship, Argo II, to search for the Doors of Death and possibly saving Percy Jackson and Annabeth Chase from Tartarus along the way. After unsuccessfully attempting to cross the Apennine Mountains due to the Ourae's hindering, Hazel leaves with her horse Arion to meet with Hecate, who offers Hazel four directions to choose. She promises the northern route that Hazel picked will work under the condition that Hazel has to practice manipulating the Mist first. Arriving at Bologna, the Argo II is raided by the Kerkopes, Passalos and Akmon, who steal Archimedes's sphere that Leo had found in Rome, among other things. Leo corners the thieves inside the Two Towers and retrieves the items alongside an agricultural book belonging to Demeter's helper, Triptolemus, and an astrolabe belonging to Odysseus but he spares the two under the condition that they head to New York City to stall the impending Roman demigods from attacking Camp Half-Blood. Frank, Hazel, and Nico meet with Triptolemus at Venice, but upon discovering Nico's status as a demigod of Hades, he forces Frank to kill the katobleps of Venice by taking Hazel and Nico hostage first before he gives them barley to make cakes that will render them immune to the poison of the Necromanteion. After Frank succeeds, the Argo II heads to the direction of the Balkans, but is blocked by the bandit Sciron, who would use his giant carnivorous turtle to devour them. By manipulating the Mist, Hazel is able to make him fall into his own trap. Her father, Pluto appears to inform her that the Doors of Death are located at the lowest level of the Necromanteion in Epirus.
Release
The House of Hades was published on October 8, 2013. It is available in hardcover, paperback, eBook and audiobook formats. Special edition versions were also released which were signed, and had exclusive drawings inside. Versions with the short story "The Crown of Ptolemy," a crossover with the other Rick Riordan series, The Kane Chronicles, and the short story "Percy Jackson and the Sword of Hades" printed at the back of the book were also released.
Characters
The Seven Demigods of the Great Prophecy
- Percy Jackson – Son of Poseidon
- Annabeth Chase – Daughter of Athena
- Jason Grace – Son of Jupiter
- Leo Valdez – Son of Hephaestus
- Piper McLean – Daughter of Aphrodite
- Frank Zhang – Son of Mars and descendant of Poseidon
- Hazel Levesque – Daughter of Pluto