Harrow examines the scarlet key won from the Response trial and finds a tiny symbol carved into it. Gideon recognizes the symbol as the mark on her own door, X-203, so Harrow leads Gideon back through Canaan House with new caution, both unsettled by the deaths of Abigail Pent and Magnus Quinn and by Teacher's warning about dangers below.

At the black door marked with Gideon's symbol, Harrow insists that Gideon use the key because the key ring is Gideon's and etiquette may matter in Canaan House. The key opens the door smoothly, and Gideon enters armed. After Harrow finds the lights, they discover a sealed, unnaturally preserved room divided into a laboratory, a training area, and a small living space with two beds.

The room appears to have belonged to a necromancer and cavalier who worked closely together. Harrow finds stone tablets containing the completed methodology from the Response trial: a theorem for transference and the use of a living soul, explicitly tied to the pursuit of Lyctoral understanding and devotion to the Necrolord Prime. Gideon finds evidence of the occupants' lives, including rapiers, a Second House seal, old personal effects, and a book inscribed, One flesh, one end. G. & P.

Harrow concludes that the room's former occupants created the theorem and the experiment below, and she resolves to study the spell so she and Gideon do not share the fate of Quinn and Pent. Gideon, shaken by Magnus's death because he had treated her kindly, contrasts Magnus's warmth with Harrow's lifelong coldness. Harrow responds that she can no longer accept being a stranger to Gideon and says she needs Gideon's trust; Gideon replies that Harrow must become trustworthy.

The tense exchange ends with Gideon bargaining for eight hours of sleep, which Harrow accepts with a condition that they resume work afterward. On the way back, Gideon and Harrow hide as Jeannemary and her necromancer pass quietly through the halls on an unknown errand. In bed, Gideon remembers a crumpled note she took from the room and reads a fragment that refers to an incomplete effort and appears to say, “give Gideon my congratulations.”