Arvelle enters her home to find Evren experiencing a severe coughing attack. She uses their last lung tonic and a healing crystal to ease his breathing. Her other brother, Gerith, is awake with worry. He reminds her of their uncle, who stole the prize money from her Sands victory six years ago—money that would have paid for Evren’s cure, a house in Nesonias, and a good education for all of them. Gerith vows to someday fight in the Sands himself in order to earn enough money for Evren’s cure.

The next day, after the brothers leave to attend makeshift classes with their tutor, Arvelle goes to a training arena to observe Fallon, a young woman whom she is helping prepare for the Sands. Carrick, a man who cares for Arvelle, arrives to warn her that a serial killer is targeting people in the Thorn and removing their hearts. He mentions Arvelle’s past relationship with a man named Ti, who abandoned her six years ago, and then proposes marriage and offers to take her and her brothers away from the Thorn. Arvelle refuses, and as a frustrated Carrick follows and harangues her, Gerith suddenly runs up in distress, telling Arvelle that something is wrong with Evren.

Arvelle races home to find Evren collapsed outside their door, suffocating. Bran stands nearby in full sunlight, callously watching as he idly holds two vials of lung tonic. Arvelle notes that Bran must be using a “sun tonic” in order to be outside during the daytime; she further reflects that such remedies are “rumored” to jeopardize a vampire’s mental health with repeated use. When Carrick arrives and confronts him, Bran smashes one of the vials. With Evren dying before her eyes, Arvelle desperately accepts Bran’s deal and gives Evren the remaining tonic. However, the remedy is insufficient. Because vampire blood has healing properties when ingested by humans, Bran feeds Evren his own blood to heal the immediate damage from the attack, although the disease remains. An enraged Gerith tries to attack Bran with one of Arvelle’s daggers, but Carrick restrains him. Bran warns that he and Arvelle will leave in two hours, and he threatens to kill both brothers if she runs.

Arvelle asks Carrick to watch her brothers and then runs to the cottage of Leon, the father of her best friend, Kassia, who was killed before her eyes as the two fought in the Sands six years ago. In the aftermath of Kassia’s death, Leon and Arvelle have become estranged. Now, she finds the still-grieving Leon’s home in disrepair and tells him that she must compete in the Sundering. Leon accuses her of disrespecting Kassia’s memory. When Arvelle explains that she was blackmailed by a vampire and is only doing this to save Evren’s life, Leon predicts that she will die in the arena because she is out of practice and has a bad ankle. To manipulate him into training her, Arvelle mentions having someone named Merrick train her instead. Leon, who understands what she is doing, concedes that he will think about being her “guardant” and officially training her.

Arvelle returns home to find Bran, Carrick, and her brothers waiting. Bran specifies the assassination terms; she must strike the emperor only when Bran signals, and she must never warn the Primus (the leader of the emperor’s elite guards, the imperius). They then renegotiate the terms of Evren’s healing; Bran agrees to cure him after Arvelle completes the Sundering, rather than after the subsequent assassination. Bran explains that he chose her because her lack of prior ambition to join the Praesidium Guard makes her appear innocent of any wrongdoing or hidden agenda now. He suddenly bites her, and when she reaches for a weapon, he breaks her wrist and then forces her to drink his blood to heal the break.

Arvelle packs a magical “whispering mirror” that will allow her to communicate with her brothers and says painful goodbyes. Leon arrives at the last moment, having grudgingly agreed to train her. They travel to Lysoria, the capital city, and meet a vampire named Elva at the station; she will escort Evren and Gerith north to Nesonias, essentially holding them hostage to Arvelle’s good behavior. After the brothers depart, Bran informs Arvelle that her first challenge in the arena will take place in less than a month.

They arrive at the ludus, the training facility for “gladians” (gladiators), which is located beneath the arena itself. The architecture favors vampires with narrow, windowless corridors. As Arvelle enters, she sees murals depicting the powerlessness of various sigilmarked gods, whom the vampires view as being inferior to Umbros, the only god they will deign to worship. She also notes a mural depicting Mortuus, the “god of ruin,” who is reputed to have been trapped below ground forever and is “feared and despised by sigilmarked and vampires alike” (41). Bran gives her a cover story and directs Leon to guardant quarters. While walking to her assigned room, Arvelle collides with a formidable vampire wearing full black armor and a helmet that conceals his face. After a hostile exchange, she instinctively pulls a knife, but he effortlessly disarms her and drops her knife before stalking away.

Arvelle enters the barracks and meets Maeva, a friendly gladian. In the dining hall, another gladian named Baldric calls Arvelle a “voidborn”—one born with no sigil or power—and reveals that his cousin Galia Volker was the one who killed Kassia in the Sands six years ago. (Kassia had delivered Galia a mortal wound in that same bout.) Standing beside Baldric is his sister, Hester, and they both vow to kill Arvelle in revenge for Galia’s death. Maeva tells Arvelle that the armored vampire (the one Arvelle collided with in the corridor) is the Primus, the leader of the imperius. A chagrined Arvelle realizes that she should have kept a low profile with the Primus due to her mission from Bran.

In a flashback, a young Arvelle comes to the tree that is a “special” place for her and Kassia, only to find that a strange boy from the noble class has usurped her spot. Angered when he wordlessly criticizes her shabby appearance, she climbs up into the tree, sits next to him, and starts an argument. She then steals his gold-buttoned jacket and flees as he laughs at her “audacity.”

The narrative returns to the present. The next morning, Arvelle uses her whispering mirror to speak with Gerith, who confirms that Evren is meeting with a healer. Later, Maeva informs her that two gladians and a guardant have recently been murdered at the ludus: more victims of the same murderer whom Carrick had mentioned in the Thorn.

All gladians are summoned to the training hall, where the emperor’s sadistic eldest son, Rorrik, publicly accuses a captured gladian named Cargyn of spying and then executes him as a warning to others, disemboweling the man with his bare hand. Arvelle is terrified to realize the extreme danger she faces, realizing that if this is what they do to mere spies, then she has no chance of surviving her mission to assassinate the emperor.

As Leon begins Arvelle’s training, he explains the brutal rules of arena combat, telling her that gladians are not allowed to exit the arena until they die or are granted mercy. A gladian’s survival ultimately depends on the will of the emperor; a raised thumb indicates mercy, while a downturned thumb indicates death. In the training hall, Arvelle is chastened to see a gold plaque bearing her name: a memorial of her Sands victory. Leon proceeds to test her strength with a heavy scutum shield, which she cannot lift, so he gives her a smaller parma shield instead. The other gladians watch sardonically, and the Primus appears and tells Arvelle to go home. When she refuses, he vows to make her leave.

Leon forces Arvelle to run 10 laps, carrying the shield. While she runs, she observes her competition, noting that Maeva is hiding her true skills, that Baldric is ruled by his anger, and that Hester has poor stamina. Others also display distinct strengths and weaknesses. After her run, Arvelle is unsettled to notice a strange spiral mark carved into a statue of the battle god Anoxian.

At lunch, the Primus physically forces Arvelle to sit at the imperius table, where she meets Micah and Neris, two imperius members. Neris, a female, calls her incompetent. The Primus, who still hides his face beneath a helmet, states that he will make Arvelle’s life miserable until she leaves; he adds that her presence is a mystery he intends to solve. He tells her to use the public appellation process to beg the emperor for permission to leave, but Arvelle refuses.

The narrative flashes back to the next time the young Arvelle encounters the boy at her tree. She learns that his name is Tiernon, or “Ti,” and that he is “obsessed with the sun” (68). When his attitude turns sulky, she decides to leave, and Ti grows angry, declaring, “I haven’t said you could leave” (68). He tries to bribe her with a golden button, but she is unmoved. When he puts his hand out and restrains her, Arvelle punches him in the face. She tries to apologize but then flees. The boy is absent from the tree the next two days she checks.

The narrative returns to the present. In training, Leon forces a sore and weary Arvelle to climb a rope, and she recognizes that he is trying to provoke her into lashing out and giving him an excuse to quit. Determined not to let him abandon her, Arvelle begins climbing. When she finally nears the top, the rope suddenly becomes slick, and she falls, scraping her hands raw. Leon, who is sigilmarked, uses his wind power to slow her descent and save her from serious injury. He confronts Hester, who sabotaged the rope with magic. When a guard intervenes, Arvelle declines to press charges, wanting to avoid making more enemies.

An imperius vampire named Nyrant addresses the gladians, announcing that the Sundering will begin in three weeks. Each gladian will receive a schedule listing their first fight date. He also announces an event for that evening, where they will meet powerful members of the empire and will have the opportunity to court potential sponsors to provide them with better gear and other advantages. The guests will include the Sigilmarked Syndicate—12 powerful, gold-crowned human governors who sponsor various gladians and place bets on the arena fights.

On the way to the healers, the Primus confronts Arvelle about her injuries. When Neris arrives and calls the Primus away, Arvelle leans back against a wall section that opens suddenly. She stumbles into a secret corridor and meets a mysterious but kind man named Jorah, who maintains the warren of hidden passages. He mentions a man named Tiberius Cotta, who promised to connect him with an imperium who might someday train him to fight. He then shows her a magical map revealing the vast underground ludus. He directs her through a passage that opens into a hidden forest garden, urging her not to linger on her way to the healers. However, when Arvelle spots a dragon-like wyvern—a species that is supposedly extinct—she freezes, watching in shock as Rorrik appears and calmly soothes the creature. When they both detect her presence, she flees back through the secret corridor, fearing future retribution from the sadistic son of the emperor. When Arvelle finally finds the healers, a healer named Axia treats her rope-burned hands.

At the sponsor event that evening, Arvelle meets members of the Sigilmarked Syndicate and sees Emperor Vallius Corvus for the first time. She observes Bran speaking with another vampire who also hates the emperor. At one point, Bran approaches Arvelle, pretending to be her sponsor, and squeezes her injured hands as a warning. The Primus suspiciously observes this interaction. When Rorrik arrives, his hostile gaze toward Arvelle confirms that he does indeed recognize her from her unsanctioned foray into the wyvern’s garden. Maeva reveals that her father is Sigilkeeper Alaric Virnia, but because she is only a bronze-sigilmarked, he has forced her to participate in the Sundering to express his disappointment in her, and he refuses to sponsor her himself. Maeva introduces Arvelle to Tiberius Cotta (the man Jorah mentioned), and she learns that he is a kind sigilkeeper who is also from the Thorn.

The event is disrupted when the corpse of a murdered gladian is found in the hall, his heart missing. The public discovery embarrasses and enrages the emperor.