The House of Hades Heroes of Olympus Bo by Rick Riordan

The stakes have never been higher. If Percy Jackson and Annabeth fail in their quest therell be hell on Earth. Literally. Wandering the deadly realm of Tartarus every step leads them further into danger. And if by some miracle they do make it to the Doors of Death theres a legion of bloodthirsty monsters waiting for them. Paperback softback