The first chapter of The Blood of Olympus was released along with the e-single of The Staff of Serapis on May 20th, 2014.  Nico di Angelo will have a POV.  On May 17th, 2014, The Blood of Olympus sneak preview leaked early three days earlier than scheduled.  In the chapter preview, Jason Grace is shown to have a POV. On June 30, 2014, Rick Riordan stated on twitter that Reyna Avila Ramírez-Arellano would have a POV.  On August 19th, 2014 the official chapter preview was released through Disney Hyperion. Disney Hyperion sent "Swag" boxes full of Heroes of Olympus goodies to famous youtubers and included a clue about the Seven, plus Nico and Reyna, on whether they will survive the final battle.
Though the Greek and Roman crew-members of the Argo II have made progress in their many quests, they still seem no closer to defeating the earth mother, Gaea. Her giants have risen—all of them, and they're stronger than ever. They must be stopped before the Feast of Spes, when Gaea plans to have two demigods sacrificed in Athens. She needs their blood—the blood of Olympus—in order to wake. The demigods are having more frequent visions of a terrible battle at Camp Half-Blood. The Roman legion from Camp Jupiter, led by Octavian, is almost within striking distance. Though it is tempting to take the Athena Parthenos to Athens to use as a secret weapon, the friends know that the huge statue belongs back on Long Island, where it might be able to stop a war between the two camps. The Athena Parthenos will go west; the Argo II will go east. The gods, still suffering from multiple personality disorder, are useless. How can a handful of young demigods hope to persevere against Gaea's army of powerful giants? As dangerous as it is to head to Athens, they have no other option. They have sacrificed too much already. And if Gaea wakes, it is game over. 
Jason Grace, Piper McLean, and Annabeth Chase infiltrate Odysseus' Palace in Ithaca using Hazel Levesque's magic, where a gathering of evil spirits or suitors is occurring. Jason, disguised as an old beggar man named Iros, is called out by Antinous who questions why Iros is there. Jason covers himself by stating that he is still running messages for the suitors and attempts to get more information out of Antinous. Eurymachus, a ghost, accidentally gives away information about how Gaea is stopping the demigods from getting to Acropolis. Eurymachus is stopped short by Antinous and is destroyed. Antinous tells Jason that Apollo no longer has control of Delphi and that Victory is running rampant, so there is no way the demigods will win. Michael Varus, the previous Praetor of Camp Jupiter who lost the Twelfth Legion's eagle in Alaska goes up to Jason and tells him that he cannot leave since someone has come to see Jason. Jason's mother, Beryl Grace, appears to him as a ghost.
Beryl attempts to convince that Jupiter made her leave Jason at the Wolf House and that she had no choice. Beryl unsuccessfully tries to get Jason to fight for Gaea, who let her out from the Underworld, and then disappears as a spirit of insanity or mania. Since the disguise around Jason is broken, all the monsters/ghosts attack. As the fight goes on, Jason is stabbed by Michael with an Imperial Gold gladius below his rib cage. Piper rushes over, defeats the ghost of Michael and tends to Jason's wounds. Annabeth runs to signal Leo Valdez on the Argo II and asks Frank Zhang to fly down and collect Jason. Suddenly, a crack appears in the stone and Juno appears to tell the heroes that they need to find goddess of victory in Olympia because she is out of control and then find the twins, Artemis and Apollo who are in hiding from Jupiter.Juno disappears before her husband Jupiter finds her, and then Jason faints.
Meanwhile, Reyna Avila Ramírez-Arellano, Nico di Angelo, and Gleeson Hedge are falling from the sky with the Athena Parthenos above the volcano, Mount Vesuvius after shadow traveling. Nico is too exhausted to shadow travel again, so Reyna helps by lending him her strength, which is a power of children of Bellona. They shadow travel one more time to Pompeii, where they lay camp for the night since Nico is unable to travel anymore. Coach Hedge takes first watch as Nico and Reyna go to sleep.
Reyna dreams of a giant following them. Then her dreams take her to where Octavian is with the legion outside of Camp Half-Blood. Octavian personally takes on the highest tile, Pontifex Maximus, which no demigod has ever done. His fellow centurion, Mike Kahale, and the legion's eagle bearer Jacob are beside him, listening to Octavian reinstate Bryce Lawrence, a legacy of Orcus, who was banished from the camp for killing a centurion and other horrific crimes. Octavian has added two dozen different murderers, thieves, and traitors into the legion since Reyna has been gone, which makes Mike upset. Mike disagrees with Octavian attacking Camp Half-Blood against Reyna's orders, but Octavian is convinced that once the Greeks are eliminated the war will be over and that he will be remembered as the savior of the Romans. Mike questions if Octavian's gift of prophecy has returned, to which Octavian defensively retaliates against.
Coach Hedge wakes up Reyna since tourists have come to visit the frozen citizens of Pompeii, but luckily the mist surrounding the Athena Parthenos is strong and wards off the tourists. By sunset, Nico wakes up and Reyna tells him about her dreams. Nico believes the dream is about a giant and to avoid it at all costs, but Coach and Reyna believe that fighting will be the best option. Nico considers asking the Hunters of Artemis', Thalia Grace, for advice, but is weary to do so. Reyna decides that she will contact the Amazons for help as well, but decides to work out the details until the next jump. Then Gaea's voice is spoken from Coach Hedge's body and multiple earthen ghosts attack.As they attack, Reyna tells Nico to get Diocletian's Scepter, so that she can command the dead legionnaires since she is a praetor. Reyna controls the dead legionnaires, but they are still out numbered. Nico, finally strapped in to carry the Athena Parthenos, shadow travels.
Back on the Argo II, Leo is working on a secret project, but is interrupted when Piper tells him that there is a meeting in the mess hall. Leo joins the others, along with Buford, the table. The seven discuss going towards Olympia, meeting Nike, and which demigods should go and meet the goddess. They decide that Frank, Hazel, Percy Jackson, and Piper should go since they are the least competitive group that will not try to outdo each other.
The four leave to go scout the area. Percy and Leo search a museum, while Frank and Hazel are looking at ruins. While waiting for Frank and Hazel to return, Leo feels uncomfortable around Percy since he got back from Tartarus and due to Calypso's old feelings for Percy. Before they could discuss it, Frank and Hazel get back accompanied by Arion who had appeared out of nowhere. The group head towards the ruins which are roughly five kilometers wide. They decide to walk through the ruins looking for something to pop up. Eventually, they head toward the Temple of Zeus where an old Nike statue used to stand. Leo and Percy provoke the goddess to come forth by challenging that Adidas shoes are better than Nike shoes.
The goddess' Roman and Greek side, Nike and Victoria, are at war with each other trying to decide which side will be victorious. The goddess challenges the the four to a fight to the death, with the Romans and Greeks against each other. Nike demands for them to fight in an arena and gives them four minutes to be present. To make sure that they get there she sends four metal statues after them. Once there, the group comes up with a plan to get out of killing each other. They decide that Hazel needs to use her power to control the underground tunnels and the power of the Archimedes' sphere if they should have any chance of defeating the goddess. After successfully tricking the goddess, they tie Nike up and she starts shouting about how they will never get the Physician's Cure after they question her about which one of the seven will die. Frank then puts a sock in her mouth and duct tape over her and they take her with them on the Argo II.
After shadow traveling, Nico is knocked unconscious and starts to dream of painful memories. As he's searching for Thalia's dreams, he ends up meeting Clovis, the head counselor of the Hypnos cabin, due to the Hypnos cabin's powerful dream activity. Nico tells Clovis to tell Chiron that they are bringing the Athena Parthenos and that he need helps tracking down Thalia. Clovis shows Nico the war meeting they had at the Big House. Clarisse La Rue is telling the campers about the defenses that they have and blames Rachel Elizabeth Dare of not being able to warn them of the giant army outside of Camp Half-Blood. Rachel defends herself by stating that Apollo's gift of prophecy is currently out of commission and Will Solace, counselor of the Apollo cabin, agrees. Ella has been too scared to mention anything about prophecies since the Romans surrounded. Clarisse demands that they attack the Roman base, which Jake Mason states is better defended than their own home. Connor Stoll convinces Clarisse to wait until Reyna delivers the Athena Parthenos like Annabeth stated. Then Nico is suddenly woken up by Coach Hedge.
After the shadow travel, the Athena Parthenos is laying sideways on the column of the Temple of Diana. Nico learns that he overshot and shadow traveled to Évora, Portugal instead of Spain and that he's been unconscious for almost 36 hours. A spirit has been wandering around the trio and wants to talk to Nico. The spirit takes Nico to chapel, where Hades awaits. Hades tells Nico the hunter Gaea is employing is Orion. Orion already has the scent of the trio and will not stop hunting them until they are captured. Hades tells Nico that Hazel knows one of the Seven will die and that wolves are currently chasing after them as well. Nico quickly goes back to where the trio have set up camp and tells them about being chased by wolves. Then suddenly Reyna's dogs are startled because wolves surround them along with Lycaon. They engage in battle and eventually manage to shadow travel away, without a clear direction of where they are going.
Meanwhile, Frank and Piper are on port of Pylos looking for the poison and failing. They make their way down to Nestor's cave after Piper charmspeaks a ghost into giving them direction. Frank goes in and talks to a man who hands him a bottle. Frank explains that his cousins, other descendants of Periclymenus, have been living there for generations. As a parting gift, the cousins gave Frank the small vile of poison. Frank has an idea of how to find a chained god in Sparta, but will not discuss it until the others are back on the Argo II. Once on the ship, Frank states that the the chained god is Ares because the Spartans believed that if they chained him up the spirt of war would never leave them. Piper unsheathes her dagger after telling them of seeing visions of Annabeth and her exploring ruins. Percy tells Leo that they should be airborne since a sea serpent is checking out the ship.
Leo, who is trying to relocate the island of Ogygia so that he can be with his love Calypso, as he swore on the Styx to do in The House of Hades is secretly rebuilding Festus inside the bulkheads of the Argo II and attempting to program Odysseus' navigation device that he picked up from the Cecropes in Bologna in The House of Hades to relocate Ogygia by fitting a crystal from Calypso's cave into it; eventually, he succeeds. In the mean time, the seven demigods are headed to Olympia to capture Nike. Only Frank, Hazel, Percy, and Leo leave the ship to get to Nike. At first she does not appear, but after Leo supports the Adidas brand of footwear, she shows up and tries to kill the young demigods. Hazel uses magic to control the Mist and confuses Nike. They are able to capture her but Nike tries cursing the demigods. However, Frank manages to gag Nike with duct tape before she manages to finish the curse. They then take her back to the ship.
Nico, Reyna, and Hedge find out that they are being hunted by Orion, the giant son of Gaea (who was born to oppose the twins Artemis and Apollo) and has turned bad after a giant scorpion kills him after being driven mad by a jealous Apollo. In San Juan, Reyna gets abducted by the Amazons and hunters of Artemis and talks to her sister Hylla, queen of the Amazons, who has gotten together with Thalia Grace to lay a trap for Orion. The sisters receive news that Orion has killed all the girls outside the base and is coming in. A battle ensues, in which some of the Hunters and Amazons are killed. To be safe, Hylla takes Reyna to their father's old house that brings back bad memories for Reyna. Orion catches them outside the building and Hylla tells him that he will fall once again at the hands of a woman. She uses her strength given to her by her mother, the goddess Bellona on him to give Reyna time to get away with Nico and Coach Hedge. As they leave, Reyna sees the ghosts of her ancestors, including the famous Puerto Rican pirate Roberto Cofresi and Captain Marion Frederic Ramirez de Arellano, a distinguished naval officer who was the first Hispanic to command a US Navy submarine, crowding the balcony of her father's old house, glaring at her and calling her a traitor and murderer.
They end up in Buford, South Carolina, a small town south of Charlotte which is the site of the Battle of Waxhaws, an American Revolution battle in which the British commander, Banastre Tarleton, also a child of Bellona, gained infamy by massacring American prisoners of war to whom he had promised quarter. Nico has managed to open up somewhat, and shares the story of a rather clumsy attempt at Hades at bonding with him, by assigning him a zombie, Jules-Albert, to drive him around; it is made clear, though not stated explicitly, elsewhere in the story that Jules-Albert is the distinguished French auto-racing pioneer Marquis Jules-Albert de Dion, who died in 1946, and that this is a chance for him to continue pursuing his passion of driving. Having loosened up, Reyna explains about the ghosts, and why she and Hylla left San Juan and why she now wants to avoid it. Her father, Julian Ramirez-Arellano, a distinguished veteran left with PTSD as a result of his Iraq War experiences, suffered a fate similar to Jason and Thalia's mother Beryl Grace: becoming infatuated with Bellona and wishing to claim her for himself, as Beryl Grace had become infatuated with Zeus, he deteriorated mentally, eventually turning into a mania, and becoming violent and abusive to where Hylla and Reyna were frequently forced to flee the house. Eventually, when Reyna was ten, she was forced to defend Hylla from their father by stabbing him with Roberto Cofresi's saber, which she realized was Imperial gold when it killed Julian.
Bryce Lawrence, who was sent on a secret mission to find Reyna by Octavian, who intends to overthrow her altogether, and has overheard Reyna tell her story, then reveals himself, summoning a horde of undead British soldiers who had participated in the massacre of American POWs to pin down Reyna and Coach Hedge and telling her that he will force her to confess and get her executed for the crime of patricide. Bryce believes that Nico is too weak to defend them, but Reyna uses the power of Bellona to strengthen Nico enough to where he destroys the undead soldiers and kills Bryce, turning him into a ghost and sending him directly to the underworld. Nico then collapses, spending three days in a coma and almost insubstantial. When he emerges from the coma, he finds that Coach Hedge has managed to summon pegasi, including Pegasus, the king of the flying horses, to take them and the statue the rest of the way to Camp Half-Blood.
Meanwhile, the seven demigods aboard the Argo II make a stop at Pylos, and Frank makes contact with his fellow descendants of Periclymenus, who was a prince of Pylos. Many of them still live in the town, and although they give him a somewhat cool reception, which he ascribes to anti-Chinese racism and his status as a Roman demigod, they nonetheless give him a gift of Pylosian mint upon his departure.
En route to their next stop, Mykonos in the Aegean, they encounter a violent storm, which, it turns out, is being generated by Kymopoleia, the Greek goddess of violent storms at sea, who has been tempted by an offer of power from Gaea. Percy and Jason descend to the sea floor to meet her at the ruins of Poseidon's original palace, where Percy is caught in a net by Polybotes, who attempts to kill him with poison. Jason points out to Kymopoleia that with no human beings left, no one will be around to fear her power, and tells her that he and Percy intend to make sure she is fully honored; she then turns on Polybotes, killing him and freeing Percy from the net. Back at the ship, Jason and Percy resolve to make good on this promise; Jason decides to seek the Roman office of Pontifex Maximus, or high priest of all the gods, in order to continue and expand upon Percy's work of making sure all the gods are honored so that more wars between the gods may be averted.
They then proceed to Mykonos, where Leo, Hazel and Frank travel to the sacred island of Delos nearby to meet with Apollo and Artemis, who have taken refuge from the internal conflict that incapacitates nearly all the gods at their birthplace. However, they are now trapped, unable to fight against the Giants or assist the Hunters of Artemis against Orion. Leo, Hazel and Frank learn that Zeus is angry with both gods, but especially with Apollo, whom he blames for appointing Rachel the Oracle of Delphi, revealing the Prophecy of Seven, and encouraging the war among the demigods by succumbing to the flattery of Octavian. Octavian's insubordination and lust for blood, power and glory has gone even further than Reyna has realized: he has spent most of the legion's money on powerful catapults called onagers built by Cyclopes. He has summoned hordes of centaurs, cynocephali (dog-headed men) and two-headed monsters to aid the Romans against the Greeks, and does not realize that they will turn on the Romans as soon as Camp Half-Blood is destroyed. Also, the ancient serpent Python is now coiled in the caverns of Delphi, blocking the spirit of prophecy; this is why Rachel Dare and Octavian can no longer see the future. Leo makes a music-making gadget as a gift for Apollo in exchange for a daisy picked by the god from the soil of Delos, another essential ingredient in a potion called "the physician's cure" which Leo intends to obtain from Asclepius. Leo realizes that he must fight Gaea with fire and that this may mean his death, but The Physician's Cure will bring him back to life so that he may fulfill the oath he swore on the Styx to return to Calypso and the line in the Prophecy of Seven that goes "an oath to keep with a final breath."
Then the Seven go to Sparta, where Annabeth and Piper visit the ancient Spartan temple of Phobos and Deimos, the gods of fear and terror, respectively, and do battle with Mimas, the Giant created to oppose Hephaestus; Piper counsels Annabeth to go with her fear instead of trying to fight it, to embrace irrational passions such as fear and love instead of trying to keep everything under control, and by so doing they defeat Mimas and obtain the makhai, spirits of fear and anger.
The Seven's next stop is the Temple of Asclepius at Epidaurus, where Leo, Jason and Piper manage to get past a menacing automaton guarding Asclepius' office in order to see him. There, they bring to the physician god the Pylosian mint, the daisy picked from Delos by Apollo, and the imprisoned makhai, and convince him to concoct The Physician's Cure for Leo; they leave with it and with a pair of glasses prescribed by Asclepius to treat nearsightedness which Jason has not realized he had.
Back at the ship, Leo programs Festus with Odysseus' navigational device to take him back to Ogygia and with a syringe which will administer The Physician's Cure to him if he dies in the fire he plans to unleash against Gaea. Hazel and Frank know of his plan, but not any of the Greek demigods, who Leo is sure will attempt to keep him from sacrificing himself.
Eventually, the Seven reach Athens, and are led to the Acropolis by Kekrops, the ancient half-snake king of Athens, who promptly turns on them, betraying them to the Giants, and they find themselves battling for their lives. While in combat, Annabeth gets a cut on her leg and her blood spills. Percy's nose is bloodied by being batted by the hand of a giant and eventually a drop of his blood rolls down his chin in the midst of battle and spills onto the ground as well, thereby waking Gaea, who appears at Camp Half-Blood, intending to destroy it.
Reyna, Nico and Coach Hedge continue to Camp Half-Blood with Pegasus and the other flying horses and land upon the deck of a yacht called the Mi Amor anchored in Long Island Sound and occupied by two mortals who, thanks to Nico, remain deeply asleep throughout the tumultuous events which follow. Immediately they are confronted by Octavian's right-hand man Michael Kahale and two other centurions, Dakota and Leila, who have been sent to arrest them, yet seem ambivalent about the task. Tyson shows up in a boat, and, mimicking Octavian's voice, orders the centurions to lay down their weapons, then boards the boat and knocks Michael unconscious. Dakota and Leila prove to be glad to help Reyna and Nico complete the mission; Nico summons his undead chauffeur Jules-Albert and he, Dakota and Leila return Michael to the Roman camp, where Dakota and Leila incite a riot among Octavian's monstrous allies in order to create a diversion. Alone, Reyna confronts Orion; aided by the power of Athena as well as Bellona, she kills him and lets him and his bow sink beneath the water.
Octavian attempts to attack Camp Half-Blood at dawn, but Dakota and Leila refuse to allow the cohorts under their command to engage, citing Reyna's orders, and Nico, Will Solace, and two others, Lou Ellen, the head counselor for the Hecate cabin, and Cecil, son of Hermes, tamper with the onagers so that the missiles they fire all detonate harmlessly in midair. This, however, provokes Clarisse to issue a challenge to the Romans to withdraw or fight; however, Reyna arrives just in the nick of time with the Athena Parthenos and sets it down by Thalia's pine tree, thereby healing the ancient breach between Greek and Roman demigods at last, and allowing the gods to come to the aid of the Seven in Athens. However, Gaea rises, and the Greeks and Romans, now united, find themselves confronting her as well as the monsters as they all sink into the earth.
With the Giants defeated, Zeus decrees that Apollo must pay for the war, and sends him to Olympus to await a punishment which is not revealed in the book; then the remaining Olympians, together with Nike, and the Seven, confer on what to do next. Gaea has risen, she must be dealt with immediately, and the only way for the Seven to get back to Camp Half-Blood in time is for Zeus to literally slap the ship back to Long Island. The Argo II disintegrates upon arrival at Camp Half-Blood, but Leo mounts Festus and engages Gaea, along with Jason and Piper. Jason summons the winds and lifts himself and Piper into the air as Leo lifts Gaea off the ground in Festus' claws; Jason uses storm winds to keep Gaea away from the earth, her source of power, and Piper uses her charmspeak to lull Gaea to sleep, as Leo sends a blast of fire against her.
Meanwhile, on the ground, Octavian reloads one of the onagers, not realizing that his robes have snagged in the mechanism so that triggering the onager will launch him to his death as well; Will, seeing this, attempts to dissuade Octavian from triggering the device, but Nico, and Michael Kahale, who has appeared on the scene, realize that they cannot stop Octavian and that in fact, it is desirable, even necessary, that he should die. Michael interposes himself between the onager and the two Greek demigods, draws his sword, and deliberately allows Octavian to launch himself to his own death along with the onager's explosive payload, which hits Gaea just as Leo blasts her with fire, doubling the fireball's destructive force and rendering Gaea, like her husband Ouranos, permanently dispersed and powerless.
With Gaea finished, the combined Greek and Roman forces dispatch and scatter the monsters, incurring heavy casualties. Nico tells Percy his secret and earns himself Percy's confusion and a high-five from Annabeth. Jason decides to stay at Camp Half-Blood with Piper but with frequent trips to Camp Jupiter. Percy and Annabeth decide to finish their senior year of high school in New York City and go to college in New Rome. At the end it is also revealed that Leo died in the explosion, but was brought back to life using the Physician's Cure. He lands in Ogygia with Festus, picks up Calypso, and flies off into the unknown.
- Jason Grace
- Piper McLean
- Percy Jackson
- Annabeth Chase
- Frank Zhang
- Hazel Levesque
- Leo Valdez
- Reyna Avila Ramírez-Arellano
- Nico di Angelo
- Butch Walker
- Lou Ellen
- Will Solace
- Clarisse La Rue
- Connor Stoll
- Bryce Lawrence
- Michael Kahale
- Argentum and Aurum
- Michael Varus
- Beryl Grace
- Julian Ramírez-Arellano
- Suitors of Penelope
- Along with The House of Hades, this book does not feature an accompanying prophecy; rather it fulfills two lines of the Prophecy of Seven.
- In Percy Jackson's Greek Heroes, it is revealed that after the events of this book, the Seven Heroes of Olympus have started the tradition of monthly Argo II reunion parties.
- Besides The Lost Hero, this is the only book where Percy does not get a point of view.