Gideon and Harrow return to the Response trial after an earlier failure. Gideon fights the regenerating bone construct while Harrow struggles, through the speaker system, to perceive the construct through Gideon’s senses. Gideon is exhausted, injured, and nauseated from the attempt, but Harrow keeps pushing rather than blaming Gideon.

Harrow finally succeeds in seeing the construct’s hidden structure and begins directing Gideon to strike precise points: the left lateral radius, a lower tibia, the mandible, ribs, and finally the sternum. Gideon follows the instructions while avoiding the construct’s attacks, and each targeted blow disables part of the mechanism without triggering regeneration. The construct collapses, leaving behind a black box that opens to reveal a scarlet key.

Gideon claims the key before Harrow can, adding it to the key ring she keeps hidden with their earlier hatch key. When Gideon mentions seeing glowing lights over the construct’s weak points near the end of the fight, Harrow is startled because Gideon should not have been able to perceive the thanergetic signatures herself. Harrow admits she does not fully understand what the experiment has revealed.

The victory also changes the emotional tone between them. Harrow, having experienced Gideon’s fighting from inside the link, openly praises Gideon’s swordsmanship and says Gideon is extraordinary with a blade. Gideon is disarmed by the admiration, but Harrow quickly tempers it by insisting Gideon is still a dreadful person; nevertheless, Harrow invites Gideon into her excitement as they prepare to use the new key.

Leaving the lab in a rare moment of companionable triumph, Gideon and Harrow head toward the hatch and ladder. At the foot of the ladder, they find two mangled bodies twisted together in death. Harrow turns one over, confirming that the corpses are Magnus Quinn and Abigail Pent, abruptly transforming their success into a crisis.