Harrowhark, Gideon, Palamedes, and Camilla reach a high, inconvenient Lyctoral laboratory whose key is held by Silas. Palamedes argues that because he completed the challenge, they are entitled to enter. Harrow reluctantly uses Palamedes’s remembered perception of the key to shape a duplicate from bone, and the copied key works.

Inside, the laboratory is a chaotic ruin of old tools, papers, sleeping bags, and research debris. Palamedes explains that the room’s original challenge involved tracing a molar to a skeleton and using its clavicle to open a box. This leads him to reveal that Canaan House’s skeleton servants are not ordinary constructs but revenants: intact spirits inhabiting preserved bones and powering themselves.

The group examines the lab’s theory stone and a tooth inscribed with a cryptic note about turning five hundred into fifty. A pinboard and binder draw Palamedes’s attention, and Camilla finds old photographs of people, including Teacher, unchanged and circled in black. The evidence suggests Teacher is another engineered corpse or spirit vessel, but the group is interrupted before they can fully determine how he functions.

A fire alarm sends them racing downstairs. In the kitchen, a sprinkler has been triggered by a smoking pan, and the skeleton servants have collapsed into piles of bones and sashes. When Camilla touches one of the bones, it dissolves into ash, confirming that something has abruptly ended their animation or destroyed the force sustaining them.

The group checks Dulcinea’s sickroom and finds Dulcinea alive but frightened, with one priest dead in a chair. Dulcinea says Teacher left about an hour earlier to lock a door. The group then heads to the priests’ wing, where they find more collapsed bones, another dead priest, and a barricade-like pile outside a closed room.

Inside the room, Captain Judith Deuteros is gravely wounded, Marta Dyas is dead, and Teacher lies stabbed through the chest and neck. Judith explains that she and Marta sent an SOS, that Teacher tried to stop them, and that Marta and Judith killed him after he attacked. Harrow reveals that Teacher was a shell filled with a hundred souls, probably a guardian rather than the murderer, and that something worse is loose in Canaan House. Judith admits the SOS reached the Imperial flagship, not the Houses, meaning the Emperor is coming; Teacher briefly revives to warn that the Emperor must not return because one of them has come back. Judith refuses rescue and stays to die beside Marta, ready in case Teacher rises again.