Helena, Soren, Sebastian, Alister, Penny, Purnell, and the rest of the rescue team infiltrate the West Island through flooded underground routes. The journey through the flood cathedral is dangerous, and Helena grows uneasy because they encounter no necrothralls in the tunnels. After emerging inside the prison, the unit moves through guards and necrothralls with lethal efficiency while searching the cells.

They do not find Luc at first, but they discover a prisoner named Vagner, whose name Helena recognizes as important to Crowther’s earlier search. Soren reluctantly agrees to bring Vagner along. On the next level, they encounter Atreus Ferron, now a lich, who taunts Sebastian about past Bayard deaths before Soren and Sebastian destroy him, though they leave his talisman behind because there is no time.

Behind Atreus’s door, the team finds Luc alive but vivisected on a medical table, restrained with nullium spikes and drugged gas that suppresses his resonance. Soren kills the remaining experimenters while Helena stabilizes Luc, removes the suppressive effects, and shocks him awake. Luc reveals he surrendered because he believed it would save Lila, and Helena and Soren reassure him that Lila is alive before dragging him into the escape.

The alarmed prison floods with expert necrothralls, chimaeras, and Aspirants. During the retreat, Purnell collapses psychologically, and when Blackthorne’s forces trap the team in the flood cathedral, Vagner shoves Purnell toward necrothralls; she flees, steps into deep current, and disappears. Blackthorne exploits Soren’s blindness and broken arm, striking him with an axe blow that kills him. Helena cannot save him by healing, so she crosses fully into necromancy, raises Soren as a fighting puppet, and orders him to protect the others until his body is torn apart and washed away.

Helena is stabbed and then seized by Basilius Blackthorne, who breaks both of her hands, reopens her wound, and prepares to deliver her to Bennet. Kaine arrives in Undying armor, kills Blackthorne by removing his talisman, and slaughters the attackers with overwhelming efficiency. When Kaine’s resonance begins suffocating everyone in the flood cathedral, Helena forces him to stop; he revives Luc, Sebastian, Penny, Alister, and Vagner, then reanimates dead Aspirants to carry them out.

Kaine takes Helena into a hidden room, where she instructs him through repairing her liver, collapsed lung, and shattered hands. His careful treatment reveals that he has learned from her healing methods, and the two argue afterward about her being used as expendable. Kaine says the reason he is helping the Eternal Flame is to keep Helena alive, not merely to avenge his mother; when Helena realizes the Council never told her that, she breaks down and kisses him.