The Blood of Olympus is an American fantasy-adventure novel written by Rick Riordan, based on Greek and Roman mythology. It was released on October 7, 2014, is the fifth and final novel in The Heroes of Olympus series. It is followed by The Hidden Oracle of The Trials of Apollo. The seven demigods of the Prophecy of Seven—Percy Jackson, Annabeth Chase, Jason Grace, Leo Valdez, Piper McLean, Hazel Levesque, and Frank Zhang—go on their final adventure to defeat Gaea/Terra while Nico di Angelo, Reyna Avila Ramírez-Arellano, and Coach Gleeson Hedge attempt to bring the Athena Parthenos to Camp Half-Blood in order to prevent a war between the Roman and Greek demigods. The novel is narrated in third-person, alternating between the points of view of Jason, Piper, Leo, Reyna, and Nico, making it the first time in the series that someone other than one of the seven demigods of the prophecy is the viewpoint character.
After the events of the previous novel, Jason, Piper, and Annabeth disguise themselves with Hazel's Mist to infiltrate Odysseus' home in Ithaca, where Gaea's resurrected souls are gathering. They learn that Gaea's army does not plan to invade Mount Olympus, but instead the Acropolis in Athens. Since the Gulf of Corinth is heavily fortified and guarded by the army, the demigods decide they have to circle the whole Peloponnese to reach Athens. When Michael Varus, one of the souls, recognizes the demigods, he forces Jason to confront his mother's insane spirit, and mortally wounds Jason. As Jason recuperates, the three demigods use Odysseus' marriage bed to summon Juno, who tells them to seek Nike and find Artemis and Apollo, both of whom have been banished by Zeus. At Olympia, Percy, Leo, Hazel, and Frank are forced to participate in Nike's deadly Olympic Games, but eventually captures her. She reveals that one of them is destined to die, and that he needs the Physician's Cure to survive, a cure that consists of Pylosian mint, the heartbeat of the chained god, and the curse of Delos.
Frank obtains the first ingredient from his shapeshifter relatives in Pylos. Piper and Annabeth obtain the second ingredient, the Makhai, from a chained Ares statue by defeating Mimas at the temple of Ares in Sparta. While sailing through the Aegean Sea, a violent storm hits the Argo II. Percy and Jason discover it is caused by Kymopoleia, a daughter of Poseidon who is working with Polybotes. Jason convinces Kymopoleia to switch sides and they kill Polybotes together. In return, he swears to become a Pontifex Maximus after the war. After reaching Mykonos, Leo, Frank, and Hazel meet with Artemis and Apollo. Apollo gives them the third ingredient, the cursed aster, and reveals that his son Asclepius is able to make the physician's cure and is at Epidaurus. Leo tells Hazel and Frank about his plan to sacrifice himself and defeat Gaea.
Meanwhile, Reyna Avila Ramírez-Arellano, Nico di Angelo, and Coach Hedge shadow-travel to Camp Half-Blood with the Athena Parthenos. At Évora, they are attacked by Lycaon and his aides, whom they defeat, and they shadow-travel to San Juan, Reyna's homeland. Reyna is captured by the Hunters of Artemis, who are working together with the Amazons, led by Reyna's sister, Hylla. A giant, revealed to be Orion, appears and massacres both the Hunters and the Amazons. Reyna, Nico, and Hedge shadow-travel to South Carolina. Reyna reveals that she killed her father's insane spirit to Nico and Hedge, and Bryce Lawrence, a legacy who was exiled from New Rome but recently reinstated, overhears. He tries to execute Reyna for patricide but is turned into a ghost by a furious Nico.
Arriving at Camp Half-Blood with the help of Pegasus and several of his brethren, Nico and Hedge head to the camp. Reyna is confronted by Orion, and she kills him with the help of her mother Bellona and Athena. Reyna reveals the Athena Parthenos, ending the warfare and rivalry. Meanwhile, the demigods head to the Acropolis and battle the army of giants, whom they kill with the help of the gods, their split personalities healed by the return of Athena Parthenos. However, the Giants injure Percy and Annabeth, whose blood wakes Gaea. The seven demigods, transported by Zeus/Jupiter, arrive and confront Gaea at the camp. Piper charmspeaks Gaea to sleep while Leo and a newly-repaired Festus bombard her with fire. With the accidental help of Octavian, who gets tangled with and fires an onager's payload that detonates nearby, Gaea is vaporized, killing Leo as well. The camps celebrate their victory together at Camp Half-Blood. Nico decides to stay in Camp Half-Blood and also reveals his crush to Percy but decides he has moved on. Jason, having been made a Pontifex, plans to visit Camp Jupiter occasionally to make offerings. Percy and Annabeth plan to move to Camp Jupiter to attend college after they graduate from high school. Meanwhile, Leo is revived by the physician's cure and arrives at Ogygia to pick up Calypso. They leave into the unknown to seek adventure.
The Blood of Olympus was released on October 7, 2014 in both hardcover and eBook formats. Disney announced that in the first printing, there were 3 million copies printed.
The Blood of Olympus received mixed reviews. While some praised Riordan's writing, as well as the inclusion of two additional POVs, some doubts were expressed over certain loose ends. According to Kirkus Reviews, "The satisfyingly cataclysmic showdowns yield to peaceful resolution at last; here's hoping it holds this time."