For years the Garde have fought the Mogadorians in secret. Now all of that has changed. The invasion has begun.
John is on the front lines of the fight in New York City. And just as the odds seem stacked against him, his best friend, a human, inexplicably develops a Legacy—and Sam may not be the only one. While the pair try to track down Five and Nine amidst the chaos, they encounter another teen who can wield abilities that were once only meant for the Garde. Whether she is a friend or a foe, however, is yet to be seen.
Meanwhile, Six, Marina, and Adam are trapped in Mexico. They fought their way into the Sanctuary and were able to awaken the power hidden within, but their preceding battle has left them without any way to reach the others. The Mogs are returning in full-force and it will take a miracle to escape. The Garde are stretched thin, fighting this war on many fronts. The only chance they have is to take out the Mogadorian leader once and for all—but his fate is now irrevocably tied with Ella’s. They can’t destroy one without the other. But if the Garde can’t find another way to stop the Mogs, humanity will suffer the same fate as the Loric: annihilation.
THEY are not hiding anymore.
THEY have begun their invasion.
THEY will take your planet by force.
THEY believe they are unstoppable.
WE can defeat them.
WE have unleashed an ancient power.
WE have turned the tide because
WE are no longer alone in this fight.
THIS IS THE BEGINNING OF THE END.
The planet Lorien was destroyed by the Mogadorians. An ennead of young children and their Keepers escaped. The first three of the children were killed. Number Four befriended humans and they fought alongside him and the other Garde, who eventually found each other after much struggle.
While hiding out in Number Nine's penthouse, they found Number Five who was revealed to be a traitor working for the Mogs. He killed Number Eight, lost his eye at the hands of Number Seven, but decided to fight for the Loric again after realizing what Setrákus Ra, the Mogadorian leader, had in store.
The Garde split up—Four, Nine, their human allies Sam Goode and Agent Walker along with her rebel FBI faction went to the United Nations to expose Setrákus Ra to the world, who had another Loric survivor Ella in his custody, treating her as his heir. It was revealed that she was bound to a charm that inflicted any damage from himself unto her, and he escaped, causing the Mogadorian invasion to begin. Sam used telekinesis to save John Smith, revealing that he has developed Legacies, a surprise to both himself and to the Garde.
The other group of Garde—Number Six, Seven, and their Mog ally Adamus Sutekh, who inherited the Legacy of Number One—went to Calakmul to activate the Loric Sanctuary, which was under surveillance of Mogadorian Phiri Dun-Ra. They awakened the Loric Entity within the temple, which briefly resurrected Eight, allowing Marina to say goodbye. She saw that the Loric energy was spreading throughout the Earth, and that they were not alone anymore.
The prologue is narrated in third person by Daniela Morales. She is a fifteen year-old Human girl living in Harlem. She is watching the news with her fifty-seven year-old stepfather, Benny. John Smith's fight against Setrákus Ra is being televised. The Mogadorians arrive inside her apartment and kill Benny. As she escapes down the fire escape, she feels an electric shock pass through her body, but assumes it is from their cannon fire. Daniela sees Mogadorians keeping count of their human captives. They attempt to capture her too, but she uses telekinesis to stop them. She has no idea how she developed the powers, but vows to use them against the aliens.
Sam Goode, John, and a group of survivors wander through a ruined New York City. It has been a few hours since the events of The Revenge of Seven. John acknowledges the wreckage of fighter jets that were shot down as they pass by. Because he has been overusing his Legacies of Lumen and Recupero, John is physically and mentally drained. Sam and John send the survivors to the surviving bridges to rendezvous with the government. The two Garde hide in a destroyed apartment, where Sam uses his telekinesis to make a sandwich. He asks how it is even possible to develop Legacies, considering he is human. John believes that whatever Number Six, Marina, and Adamus Sutekh achieved at the Sanctuary has affected Sam. Later, they see a TV news broadcast of two very powerful beings attacking one another, wiping out Mogadorians in the process. They know immediately that it is Number Five and Number Nine and go to track them down in Union Square.
In Calakmul, Six, Marina, and Adam exit the Sanctuary. Six contemplates on how she expected the world to be changed when they arose from the temple. Adam asks what their next move is, but Six says she hoped that the Loric Entity would answer, as they spoke to it before after it possessed Number Eight's body. The three Garde realize that the domed energy field surrounding the Sanctuary is no longer there, which Marina believes is due to its energy being diverted somewhere else; she is more faithful in Lorien having exited the Sanctuary. Six and Adam want to return to civilization in order to find out what the Entity has done. However, they find that Dust has been paralyzed and cannot be healed and that the conduit generator for their Skimmer is missing. The culprit is Phiri Dun-Ra, whom Six left alive, now lurking in the jungle. The Garde decide to hunt her down in order to retrieve their tech.
John and Sam make their way to Union Square, which has been abandoned in the destruction. While there, the two boys come across a squadron of Mogadorians that appears to be spooked, focusing their weapons at a bank. They kill the Mogs and John uses his Lumen to see whoever is inside. Instead of finding Five or Nine, they discover Daniela. At first John believes that she was holed up inside with one of the Garde, until realizing that she herself has Legacies. Finally able to speak with other Garde, Daniela asks why John "picked" her to be enhanced by Legacies. He has no idea, and believes that she can help them win the war. However, he is surprised by her unwillingness to help them fight because of her lack of knowledge about the Mogadorians. Before either Sam or John can explain, the Anubis flies overhead and begins to destroy the skyline.
At the Sanctuary, Adam plans the capture of Phiri Dun-Ra. While in motion, Six asks who Adam was referring to aboard the Skimmer earlier, in The Revenge of Seven, when he said she reminded him of someone. He admits he was referring to Number One. When she accuses him of stealing One's Legacy and being sent on a mission to "stalk" her, Adam tells her that he had a deep, psychological connection to One, which was why he is okay with being close to another Garde physically. After Marina captures Phiri, an impressed Adam tortures the Mog for information on the conduits. She unintentionally reveals their location inside a bag tucked in a log. Adam opens the bag, but it turns out to be a bomb, destroying the conduits and sending shrapnel flying everywhere. When Adam attempts to use his Legacy of Terric to absorb the explosion, he is hit in the torso by the blast at close range.
Marina desperately attempts to heal him, but portions of Adam's torso almost disintegrate, despite him being Trueborn. She finally completes the process, and then heals Six's impaled leg. Adam expresses his desire to kill Phiri now that they are stranded. To wait out their decision, Adam hacks into the Mogadorians' global communications' systems so Six can hear about what is happening around the world. Adam translates that the Mogs are progressing in the invasion, which began while they were inside the Sanctuary. He tells her that the Garde-assisted resistance in New York has failed, and that they have taken the city.
In New York, the Garde escape into a flooded subway station, where they used their combined telekinesis to keep the ceiling from collapsing. John passes out from overexertion of his Legacies. Ella induces him into a telepathic dream. He watches in horror the augmentation procedure given to her after she was brought back aboard the Anubis. Ella, outside of her physical body, shows Setrákus Ra dropping the pendants into a Vatborn egg. She tells John about her Legacy of Precognition, enabling her to predict the future's infinite outcomes. She explains that her vision in Washington DC, from The Fall of Five, is now nonexistent. However, she does see herself dying in the outcome where they win. Ella warns John that the Anubis is headed to Calakmul, and tells him to warn the others. He wakes up after six hours. greeted by the United States military. A soldier tells him, "Agent Walker would like a word."
The soldiers take them to a safe zone outside of the city, where Daniela departs to search for her mother among the survivors. Walker briefs John about the twenty-five warships each over their own major city, the tens of thousands of casualties in Beijing when they attempted to break through enemy shields, and the cities where it appears that "the Mogs are taking it easy on them." Setrákus Ra is falsely claiming the Loric as "alien terrorists" that are the cause for the Mogs to fire on the human cities. He also asks that within forty-eight hours, the Garde must be turned in along with humans who have begun displaying signs of Legacies as well. John does not tell Walker whether or not this is true. At first he believes that she is trying to capture John and Sam, but Walker reassures John that she, and currently the United States, are on his side. He watches a promotional video Sarah made, whom later calls him and tells John about GUARD.
Back in Mexico, Adam is attempting to fix the Skimmer. However, he is not an engineer, so his progress is trial and error. Phiri tries to turn Six and Adam on each other by claiming Adam should have been able to fix the Skimmer by now, and that he is too much of a coward to face the battles to come. Adam gags her and contemplates killing her before going back to his workbench. Marina fears that they all may become cold and merciless if the war intensifies. Six manages to call Sam, and is happy to hear that he has received Legacies. However, their reunion is cut short due to the Anubis closing in on the Sanctuary. Adam explains to John how to remove the cloaking devices from the Skimmers and the warships.
Marina wants to stay behind to protect the Sanctuary while Adam wants to leave to be safe from the Anubis. They argue, and he asks which one will kill Ella in order to break the Charm cast by Setrákus Ra. When Adam mocks Marina's faith in the Entity, she shoots an icicle at him and calls him a monster. He apologizes to Six, who supports the option of running into the jungle. Six and Adam plan to trick Setrákus Ra and steal the Anubis, saving Ella in the process. They begin rigging C-4 to the Skimmers in front of the temple and place cannon turrets in the forest. Adam and Marina make amends, and they use their Legacies to block access to the Sanctuary's staircase by digging a massive pit. However, they are interrupted by a spaceship speeding toward them.
However, the ship is identified as of Loric origin, confusing the Garde. They realize it is the same ship that flew them to Earth. Marina believed the craft to have been destroyed. When Mark James, Sarah Hart, and Bernie Kosar deplane, Marina and Six board the ship to meet Lexa. She explains her being there and why she stayed hidden for so many years instead of joining the Garde earlier, and that her friend Zophie was killed trying to find the original pilot of the ship and Zophie's brother, Janus. The group makes plans to defend the Sanctuary and set a number of other traps. Lexa hides the ship in the jungle away from the temple site, just in case. The Anubis arrives early, Ella alerting Six and Marina that if they do not run, someone will die. The main cannon of the Anubis destroys the entire temple.
Back in New York, John gets a cryptic message from Number Five that if he does not come to the Statue of Liberty by sunset, he will get another scar, indicating that he has captured and will kill Nine. John, Sam, and Daniela, who rejoins the group after failing to find her mother, depart for Liberty Island. They bring Walker and an FBI team along with them to apprehend Five in case he tries to attack. However, it is revealed that he was in fact impaled with a traffic signpost by Nine, implying that it was his own life that was in danger, as he could not heal the wound and had to adapt to the material of the sign. He allows John to make the choice of whether he lives or dies, reverting back to his normal flesh and allowing the wound to take its course.
John asks for Sam's help, who refuses. Daniela assists John instead in saving Five's life. After the two Garde are healed, a hulking creature which Daniela dubs a "Mogasaur" and Sam compares to a "tarrasque" emerges from the Hudson River. Before they can attempt to stop it, tendrils of Loric energy erect from the ground and put the Loric and Human Garde into a brief catatonic state. Back at Calakmul, the smoke clears and the temple is completely destroyed. However, the well where the Phoenix Stones were committed to the earth remains. It is revealed that Ra simply wanted what was beneath the temple rather than taking the risk of going down the steps. Ra deploys a machine to extract the Loric energy from the Earth, resulting in a guerrilla battle against the Mogs.
Adam has his blade to Setrákus Ra's throat, threatening to kill him if he does not shut down the machine. Ra claims that Adam's Legacy is simply the product of Mogadorian science, but Adam does not relent and does not seem to care that he will kill Ella in the process of killing Setrákus Ra. Adam never gets the chance because Ra is too fast and, using the distraction to his advantage, breaks Adam's face. Marina attempts to heal him while Ra and Six prepare to duel. Ella tosses herself into the well, killing herself and dismantling the extraction device. Six takes a stone and strikes Ra across the head, proving that the charm is broken when he bleeds. Before any more blows are struck, Ella's body begins to emit azure light from every appendage, which connects to all of the Garde, including Adam and Ra, pulling them into a mass telepathic link.