Summary: The character continue to get deeper into the mythology and danger.
This is essentially the 9th fully book (with a couple more short story collections) of the Percy Jackson series. This second series Rick Riordan has expanded his available mythology so that both Greek and Roman mythologies are available. I am far outside my own depth and knowledge at this point. That is not a problem because Riordan does not expect the reader to know everything. But there are more and more minor figures involved in every book.
At the end of the last book, Percy and Annabeth were sucked into Tartarus (the deepest place of the underworld where the Titans and other monsters get banished). The rest of the crew has to try to get to the door to the House of Hades to both let Percy and Annabeth out and to seal the door to keep the monsters from over running the world and to stop Gaia from waking up.




