Lyra falls screaming into the abyss. A red, crystalline crack appears and swallows her, transporting her to Hades’s water garden in the Underworld. A past version of Hades appears, angry at her unexpected arrival. Overwhelmed with relief, Lyra kisses him. He kisses her back, then pulls away, confused—he identifies her as his “future Lyra” (10) by her long hair and notes that in this timeline, she is currently in the middle of Poseidon’s Labor during the Crucible trials. The red crack reappears and pulls Lyra back into the abyss.

While falling, Lyra attempts to teleport back to Boone on the bridge. The effort partially succeeds—she stops falling but lands in a recreation of her old bedroom in the Order of Thieves’ den in San Francisco, wearing her old mortal clothes. A woman appears, whom she recognizes as Hestia, the goddess of home and hearth, who supposedly died during the Anaxian Wars. Hestia welcomes her to the Labyrinth.

Hestia’s projection explains that the only way out of Tartarus is to open the Lock. When Lyra interrupts, the projection glitches like a malfunctioning recording. Hestia announces that the Lock tests innocence. It can only be opened by giving up one’s deepest unfulfilled desire. She strips Lyra of her goddess powers and explains that she will be granted her deepest desire through false memories. To unseal the Lock, Lyra must willingly reject this wish fulfillment. Hestia disappears. The room takes on a rose-colored haze, and Felix, Lyra’s old boss in the Order, knocks on her door. When Lyra opens it, she finds him standing with her estranged parents, Brad and Jessica Keres.

Lyra realizes the Lock is granting her childhood desire for family and belonging. Resisting the illusion causes sharp pain, while accepting it feels warm and real. She steps through the doorway into her parents’ arms, and her true memories fade, replaced by the belief that Hades and Tartarus were only nightmares. Felix calls her a “master thief” (21), and false memories of her prowess fill her mind. Lyra has a fleeting vision of Felix with jagged, inhuman teeth. As her parents lead her away, Boone appears, and new memories form: In this reality, they are partners and best friends.

Boone appears crisp and clear in the illusion, unlike the hazy surroundings. He pulls Lyra aside, expressing concern. The phrase “the gods have plans for us” (25) triggers a flash of pain and a brief memory of Hades’s silvery eyes. Boone reveals that he paid off his debt two years ago but stayed in the Order for her. Lyra is filled with happiness at being wanted by both her family and her friend. As Boone leaves, she looks back at her parents and has a momentary vision of them with blank spaces where their eyes should be.

Lyra dismisses the vision as a trick of the light. She finds herself suddenly in the hallway of her childhood home, the walls lined with photos of her at different ages. In her old room, she has vivid memory flashes of a king-sized bed with gray silk sheets and the scent of chocolate and smoke—Hades’s scent. Her father tells her that her birth name was Alani. The memory of the bed returns stronger, bringing with it the sensation of a strong arm around her and a deep sense of happiness.

Lyra sees Hades in bed with her, looking at her with adoration. The vividness of this memory shatters the illusion, and her true memories return. She realizes her desire for a future with Hades is now stronger than her childhood desire for her parents’ love. She calls out to Hestia, rejecting the alternate life. Her parents’ faces melt away, revealing monstrous creatures called Nightmares. Lyra realizes Boone’s presence is real, and he has been trapped in the Lock with her. She whistles a thieves’ signal and tackles him, breaking him out of the illusion. The house dissolves into a vast stone chamber littered with bones, and they fight the two Nightmares together. As one Nightmare holds Boone overhead, a red time crack swallows Lyra and deposits her in Hades’s penthouse office where she grabs one of her axes from a shelf. She returns to the exact moment she left and uses the axe to disable both Nightmares. An archway opens in the wall, revealing assembled Titans.

Flying Nightmares approach from above. Lyra and Boone sprint through the archway, and Hestia’s voice announces her Lock is unsealed. Their powers return in a painful surge. Mnemosyne, a masked Titaness, notes the unusual manner of their return. Iapetus, a Titan in tourist attire, questions how Lyra has a weapon. Before anyone can answer, the Nightmares bow to Lyra. A voice in her head pledges their allegiance, calling her “Mistress” (43). The Nightmares depart, and the archway seals, now bearing a glowing golden symbol of Hestia.

Lyra and Boone are surrounded by nine Titans in a large cavern. Cronos and Oceanus are absent. Iapetus reveals there is more than one Lock, and suggests throwing Lyra into the next one. Lyra identifies the serene Titaness with silver eyes as Rhea, Hades’s mother. As the Titans prepare to attack, Rhea steps in to protect them. Lyra notices Boone has vanished, and then hears him whisper that he is invisible and has a plan.

A red time crack transports Lyra to Olympus during the Crucible trials, just after Athena’s Labor. She witnesses the moment when Hades breaks her heart to preserve her curse and protect her from the sirens. The experience makes her doubt his motives. Lyra confronts the past Hades, who is resentful, claiming a future version of her told him to be cruel to her. He kisses her passionately, and her doubts momentarily dissolve. Comforting Lyra, he calls her “my star” (56). As the time crack reappears, she clings to Hades until she is pulled back to Tartarus.

Hades pounds on the Gates of Tartarus furiously, vowing to destroy the world to reach Lyra. To stop him, Cerberus and Demeter use their powers to bury him. Hades tries to command them to release him, but realizes he cannot, as Lyra is now Queen of the Underworld. Charon and Cerberus reason with him, reminding him that Lyra would not want him to cause mass destruction. Hades remembers Lyra’s strength and her belief that fate can be changed. He resolves to find another way to save her.

Lyra returns to Tartarus, disoriented. Rhea confirms she time-traveled and explains that Cronos broke time long ago, creating the red crystalline cracks. Iapetus insists on putting Lyra in the next Lock. As the Titans move to attack, Boone makes them both invisible. A bell chimes, and the Titans go pale with fear. One Titaness liquefies into water as the Titans scatter into tunnels. Rhea stays behind long enough to warn Lyra to hide and not let the invisible Pandemonium touch her, then she flees.

Boone keeps them invisible while they wait for danger to pass. They do not see the Pandemonium, but they witness a Titaness named Theia transform into a feral, monstrous state. Lyra and Boone sneak past her into a dark tunnel. They emerge into a vast, fiery wasteland containing four enormous Pillars of the Cosmos—Earth, Sky, Ocean, and Fire—which appear to be the source of those elements for the world. Rhea appears, having anticipated their path. She cancels Boone’s invisibility effect and offers to hide them.

Rhea leads them to the Pillar of Earth and opens a secret chamber within it. She explains that, when the bell chimes, the Pandemonium emerge from the onyx obelisk near the bridge. They are invisible, and their touch drives Titans mad for about a day. Cronos pulled Lyra and Boone into Hestia’s Lock to save them, but did not have time to escape. The Titans have since subdued him and locked him in a cell as a form of quarantine. Rhea confirms that the Titaness of prophecy, Phoebe, has foreseen that Lyra is the Titans’ only hope of escaping Tartarus. Before leaving, Rhea warns them that changing the past via the time cracks can reset time for everyone.

Lyra spirals emotionally, realizing Hades never told her about her previous appearances in his life. Meanwhile, Boone maps out Tartarus and states that he cannot escape without her help. His words break through Lyra’s despair, and she refocuses. A red time crack appears inside their chamber. Boone grabs Lyra and pulls her into it.

Lyra arrives alone near an ancient, colorful building by the Mediterranean Sea. She follows the sound of laughter and discovers a younger Cronos, Rhea, and their young children—baby Zeus, Poseidon, Hera, Hestia, and Demeter—having a happy family picnic. She watches Cronos lovingly play with baby Zeus. A teenage Hades appears and recognizes Lyra.

Hades recognizes Lyra from dreams and a childhood memory of her as a guardian angel. He teleports them to a secluded spot to question her. Hades lives in fear of his powers, as his touch sends mortals and gods permanently to the Underworld. However, when Lyra touches his arm, she does not die, and he realizes he can control his power around her. Overwhelmed, he bursts into blue flames, but her words, “You’re not a monster” (89), douse them instantly. Lyra tells Hades that he will master his powers and needs to have faith in himself. As she begins to fade away, she tells Hades her name.

Lyra reappears in the hidden chamber, where Boone has been waiting through periodic earthquakes. Vines suddenly burst through the wall, creating an exit. Outside, they see the vines on the pillar are moving upward. Persephone, a beautiful goddess with rose-tipped hair, appears suspended by the vines and smiles at them.

Boone accuses Persephone of setting a trap for Lyra at the gates. She confirms that Cronos was sent in her place but refuses to explain why, citing the danger of triggering a time reset if Lyra learns too much too fast. Persephone says she needs to show them something important. Vines carry them up the side of the pillar to a balcony near the cavern ceiling, where the surrounding stone is covered in scorch and claw marks from the Titans’ failed escape attempts over millennia.

Persephone shows them a large golden crack in the stone that appeared the first time Lyra came to Tartarus and grows larger with each time reset. Similar cracks mark the other pillars, revealing that Tartarus itself is breaking apart. Persephone stitches the crack closed with vines and flowers. She tells Lyra she must save them all and must learn to trust them. Then Persephone shoves Lyra into Iapetus, who was hiding behind her. Iapetus captures Lyra, jumps off the balcony, and runs with her through the tunnels to the bridge. Dangling Lyra over the abyss, he says she will thank him if she survives, and he drops her.

Lyra falls into the abyss and lands in a large arena resembling the ancient Roman Circus Maximus. Boone appears beside her, having jumped to follow. They are dressed in ancient-style clothing and armed only with knives. A copy of Hades appears, looking to be in his early twenties. Unlike Hestia’s simple recording, this copy is interactive. He states that Lyra has attempted his Lock many times before, but this is Boone’s first. Lyra asserts that the real Hades loves her and made her his queen. The copy seems momentarily affected, but begins the test.

The Hades copy strips Lyra and Boone of their powers and introduces the test: They must win a seven-lap chariot race against his team of horses made of smoke and blue fire. They can summon horses from any god’s power. If they win, the Lock opens; if his team wins, they die. Lyra summons horses made of Nike’s power of victory—winged, solid gold steeds—and the race begins. After the first lap, Lyra sees the Hades copy watching from a pavilion. She vows to win to save the real Hades from the guilt of her death.

Boone appears driving a team of glowing, pixelated horses drawn from Hermes’ power of digital speed. After the second lap, skeletal hands burst from the ground. Zombies destroy Lyra’s golden horses and throw her from her chariot. Boone swoops in and pulls her into his chariot. Lyra summons a new team of horses made from Poseidon’s ocean waves.

Lyra commands her water horses to attack Hades’s smoke team, slowing them down. After the fifth lap, zombies destroy Boone’s chariot, and he is dragged by his reins until Lyra throws her knife to cut him free. He reappears riding invisible horses drawn from the Anemoi winds. Zombie hands fling Lyra from her chariot. She orders Boone to keep going and summons mares made from Aphrodite’s power of lust. Hades’s stallions halt, distracted. Boone’s wind horses blow past the finish line, winning the race. The zombies and all horses disappear.

Boone and Lyra celebrate their victory. The Hades copy tells her that the only way out of Tartarus is to unseal seven Locks made by Hestia, Hades, Demeter, Poseidon, Hera, Zeus, and Aphrodite. Lyra has the power to do this because she was once human. He suspects that the Titans are causing time resets to keep Lyra returning, but she has never succeeded in unsealing all seven Locks in any previous timeline. The Hades copy expresses doubt that the real Hades loves her, then kisses her. The kiss feels empty to Lyra. As she leaves, he warns her not to let the Titans out.