For Percy Jackson fans, it''s been a long year since the cliffhanger at the end of The Mark of Athena(2012). Now Riordan picks up the story and carries it to a rewarding conclusion, with the main set of characters reunited and preparing themselves for the final showdown with Gaea. Throughout the book, Percy and Annabeth make their harrowing way through the underworld to the Doors of Death. Meanwhile, Hazel, Leo, Frank, Piper, Jason, Nico, and Reyna endure their own perils, all the way through to the story''s climax. In addition to experiencing growth spurts, several of the teen demigods take significant steps toward understanding their powers, accepting their feelings, trusting each other, and taking responsibility for leadership. Adventure fans will relish the action as their heroes confront formidable foes, while readers who have come to love the characters will enjoy following the different individuals as they take the stage in scenes that are usually dramatic, often witty, and occasionally surprising. A satisfying, penultimate entry in the Heroes of Olympus series. - Carolyn Phelan-Booklist Online