Harrow leads Gideon from the corridor to the pool room, seals the doors with skeletons, and insists they get into the salt water because Ninth House secrets may only be spoken there. Harrow admits she knew early that Dulcinea’s cavalier Protesilaus was a corpse-puppet: she found him already murdered, pushed the necromantic theorem until the body fell apart, took the head, and hid it. Gideon confronts Harrow for withholding this before sending the Fourth teens into danger, and Harrow admits she panicked and feared Gideon would trust Dulcinea over her.

Gideon asks who is responsible for the murders, but Harrow cannot identify the killer. Harrow reasons that if the deaths are connected and caused by a living adept rather than revenants or the facility itself, then someone at Canaan House must be responsible. Harrow lists the remaining Houses, Teacher, and the priests as possible suspects, while noting that Palamedes and Camilla are the most logically capable despite lacking any clear motive.

Gideon then asks about the childhood plague that killed the Ninth House children. Harrow reveals it was not an accident: Harrow’s parents and great-aunts murdered two hundred children by pumping organophosphates through the cooling system so the simultaneous thanergy would ensure Harrow’s conception as a powerful necromancer and heir to the Locked Tomb. Gideon was meant to die too, but survived ten minutes of nerve gas unharmed, which is why Harrow’s parents feared Gideon afterward.

Harrow explains that she has always known she was created at the cost of an entire generation and considers herself an abomination, though she says she would do it again to preserve the Locked Tomb. Harrow reveals that at age ten she opened the Tomb, intending to judge whether her existence was worth it and then kill herself if not. Gideon’s report to Harrow’s parents did not cause their deaths in the way Gideon believed: Harrow says her parents killed themselves from fear and shame, tried to make Harrow hang herself too, and Harrow survived because she could not go through with it.

When Gideon apologizes, Harrow explodes, confessing that she spent years abusing Gideon because Gideon’s survival and pity exposed Harrow’s own guilt and self-hatred. Harrow calls Gideon her only friend and says she is undone without Gideon. Gideon responds by holding Harrow, then renews their bond as necromancer and cavalier with the words, “One flesh, one end.”

Harrow asks Gideon, if Harrow dies, to return to the Ninth House and protect the Locked Tomb. Harrow describes the Tomb as a salt-water sepulchre containing the frozen corpse of a chained girl with a sword, whose face made Harrow decide to live forever in case the girl ever woke. Later, in their room, Gideon asks whether Harrow tried to kill her in the shuttle incident; Harrow swears she did not and explains the plan was only to disgrace Ortus and Glaurica. Harrow admits she did not believe Crux’s claim that the shuttle exploded by accident, implying Crux destroyed it out of zeal against disloyalty.