Brown includes an expansive Dramatis Personae, showing the most critical characters throughout the series. The Dramatis Personae is divided into groups listing the members of the rebel Solar Republic, the oppressive Society, the Rim Dominion, the Obsidian, and other non-categorized characters.

Key members of the Republic include the Sovereign Virginia, Darrow, Pax, Sevro, Kavax, Thraxa, Cassius, Matteo, and Quicksilver. Atalantia, Lysander, Atlas, Ajax, Pallas, Cicero, Julia, Rhone, Glirastes, Exeter, and Pytha are listed among the living and most relevant characters in Light Bringer. The Rim Dominion includes Dido, Diomedes, and Helios; important Obsidians include Volga, Volsung Fa, and Valdir, and key unaffiliated characters include Aurea; Appolonius, or the Minotaur; and Lyria.

Darrow and the other surviving members of the Free Legion who were saved by Cassius are hiding on a “trash moon,” repairing the Archimedes and waiting for Cassius and Aurae to return. Unable to communicate with anyone outside of their hidden base, Darrow has no idea what is happening in the rest of the solar system. He fantasizes about returning to the war but feels powerless: “The anger that once made planets tremble is now toothless” (4). He worries that his failure will result in the Society rising back to power.

Aurea left Darrow with a book, The Path to the Vale. He is frustrated by the gesture but reads it, drawn to the book’s wisdom. Thraxa calls Darrow, who is welding the Archimedes, telling him and the rest of the workers on shift to come inside. Before going in, Darrow looks toward his home—Mars.

Darrow and the others worry that they’re not receiving updates about the war: “Together, we make a sea of worry under the dim chemical lights” (9). He goes to Harnassus, where they discuss Cassius and Aurae. Darrow goes to Screwface, who has been closely surveilling the area for Atlas au Raa, the Fear Knight. Darrow confronts Screwface about his bitterness, ordering him to stop complaining in front of the remaining soldiers.

Leaving Screwface, Darrow practices fighting while a computer reads The Path to the Vale in Virginia’s voice. Afterward, he records messages for Virginia and Pax. The proximity alarm sounds, and Screwface calls and announces a Votum ship approaching.

Darrow joins Thraxa, and the two prepare to fight the incoming ship; however, Screwface announces that the newcomers are Cassius, Aurae, and other friends, including Colloway Char. Colloway tells them that the Republic still holds Mars; that Virginia, Victra, Kavax, and Kieran are alive; that Sefi is dead; that the Obsidians, along with the Ascomanni, are being led by Volsung Fa; and that the Free Legions left on Mercury have been either killed or enslaved.

Cassius announces that he has brought helium to power their ships and that Sevro has been sold at an auction.

Darrow watches footage of a mangled and terrified Sevro being sold to Apollonius au Valii-Rath, or the Minotaur. Apollonius bought Sevro to lure Darrow to the Dockyards of Venus. Darrow wants to save Sevro, but the others want to return to Mars. Privately, Cassius and Aurae agree to help Darrow save Sevro, and Cassius admits his guilt over relishing his life as a Gold in the Society.

Thraxa and the others catch Darrow, Cassius, and Aurae trying to sneak away. Although they try to stop Darrow at first, the soldiers begrudgingly let him pass. Thraxa gives Darrow her razor, Bad Lass.

Lysander is forced to host games on Mercury. Glirastes, the Master Maker, speaks of how the people love Lysander, and Rhone, the Dux of Lysander’s soldiers, complains about the expense. Later, Glirastes admits that the games are expensive and that the guests they attract are troubling. Lysander argues that he is not being manipulated and that he has been secretly sending war fleets to Apollonius. Glirastes implores Lysander to focus on rebuilding Mercury, but Lysander counters that he needs more power.

Lysander attends a chariot race, hoping to secure the support of the Carthii family—a major Gold Venusian house. Valeria au Carthii wants the Venus Dockyards, which have been given to Apollonius, returned to the Carthii family. Cicero au Carthii prepares for the chariot race, although he is not supposed to participate.

Darrow, Cassius, and Aurae fly the Archimedes toward Venus, hidden by the “stealth hull” on the ship. When they arrive, Darrow and Cassius disembark, while Aurae takes the ship to plant an atomic weapon in the Dockyards. Before leaving, Darrow talks with Aurae, who hints at an ulterior motive for joining them: “‘I am here for Sevro […] that is the truth. Not the whole truth, but it is all the truth that matters, because it is all the truth that is useful” (49).

Darrow and Cassius jump from the ship to the Dockyards, entering an arcade for Greens—the technologically skilled, low-Color caste. There, they coerce one of the Greens into pulling up surveillance footage to locate Sevro. Cassius and Darrow fight their way to Sevro’s cell, but the person in the cell is an imposter. They are captured by Apollonius.

Lysander speaks to Cicero after Cicero wins the chariot race, though he does not scold him harshly for competing: “I’m careful not to tread on my friends’ spirits these days” (58). Cicero warns Lysander to be “gentler” with Glirastes, who is wracked with guilt after helping Darrow use the Storm Gods—massive atmospheric terraforming machines—to engineer a cataclysmic storm on Mercury. Tharsus approaches with the news that Apollonius has Darrow and Cassius. Lysander is shocked, having believed that Cassius, his old mentor, was dead.

That night, Lysander meets with Helios au Lux, a rising Gold commander known for his fanatical loyalty to the Core, and Diomedes au Raa, the Storm Knight. Diomedes apologizes for lying about Cassius’s death, admitting that he spared Cassius in a show of respect for Cassius’s honor. Helios and Diomedes are on their way to a summit held by Atalantia. Helios resents the war, wanting to return to isolation in the Rim. Atlas joins them, and Lysander is troubled by the fact that he did not know Atlas was on the planet. Lysander invites Atlas to the launch of the Lightbringer, his newly renamed flagship—formerly Darrow’s Morning Star—but Atlas declines. He tells Kyber to follow Atlas. The next day, Lysander visits Glirastes and tells him that Darrow has been captured.

Darrow, who has been treated well, and Cassius, who has been beaten, are taken to Apollonius, who has an unexpectedly large army. Apollonius enters, refuses to bring out Sevro, and announces his desire to duel with Darrow. Darrow threatens Apollonius with the hidden atomic bomb, but his soldiers have already found the device.

Apollonius pours out Martian soil for their fight, and Darrow continues to press him for information about Sevro. Darrow struggles, which frustrates Apollonius: “He steps clear and watches me as if with a broken heart” (80). As Darrow goes to finish the duel, a bomb detonates.

A smiling Apollonius dispatches soldiers to investigate the bombing, and Darrow realizes that Sevro escaped. Asmodeus au Carthii calls Apollonius, announcing the Carthii family’s plan to exact revenge against Apollonius for bombing the Dockyards. Apollonius prepares for battle.

Darrow and Cassius follow Apollonius, but they are trapped in a hallway as the Carthii forces approach. Berserker fighters—highly trained Obsidian warriors—attack, and Darrow and Cassius fight their way through until Sevro arrives in a StarShell, a large, mechanized, full-body suit of armor and weaponry, helping them escape. They call for Aurae, who comes for them with the Archimedes.

Lysander hosts a ceremonial launch of the Lightbringer. With Pytha piloting the ship, it successfully launches. Glirastes introduces Lysander to Pallas au Grecca, who has come in Julia Bellona’s stead, as Julia is prioritizing her allyship with Atalantia. Julia is a powerful Gold matriarch and the mother of Cassius.

Rhone calls to tell Lysander about the attack on Venus. Lysander admits to Valeria that he has given Apollonius forces to keep Valeria from killing Tharsus, Apollonius’s brother. He says that he will give her the Dockyards if she keeps his secret, and she agrees. Atlas and his Gorgon forces arrive, and Atlas theatrically kills Tharsus and orders Lysander to report to New Sparta. Glirastes begs Lysander not to go, but Lysander agrees, parting tenderly with Glirastes. Lysander leaves with Atlas and is beaten by Gorgons.

Darrow feels both tension and security with Sevro, who is thin and haggard and wears a necklace of decaying ears. Sevro discusses escaping from Apollonius and killing people, but he refuses to talk about the torture that he and his elite unit, called Howlers, endured from the young clone of Adrius au Augustus. Cassius joins, and Darrow intervenes when Sevro shows Cassius hostility for killing Fitchner, Sevro’s father and the creator of the Sons of Ares. Darrow also apologizes to Sevro for forcing him to choose between following Darrow and staying with his family. Sevro understands but does not yet forgive Darrow, arguing that he can no longer participate in the war and describing what it was like to witness his Howlers be tortured and killed by Adrius: “They did smell like bacon, Darrow. The Howlers. I lost them all” (107).

Aurae joins them and gives Sevro a holocube with a message from Athena, the leader of the Daughter of Ares, which is active in the Rim. The message calls for Sevro to come and take his father’s place. The message includes a pre-recording of Fitchner imploring Sevro to step into his place. Aurae, a Daughter of Ares, admits that she has lied but explains that she does not have much information about the Daughters, as she has been deep undercover for years, serving as an enslaved person to the Raa family.

Later, Darrow goes to Sevro’s room, staying with him and reading to him until he falls asleep. Darrow finds Cassius, and Cassius urges Darrow to keep his spirits up, telling him that Virginia still believes in him. Darrow encourages Cassius to stand up to Sevro, and Cassius offers to help Darrow train for battle.