Din Kol rushes to the Apoth tower, where Ana Dolabra waits blindfolded in Immunis Nusis’s dark office. Nusis is slumped dead at her desk in a pool of blood. At Ana’s direction, Din checks the body and finds a small purplish puncture behind Nusis’s ear, matching the other “twitch” killings; Nusis’s safe is still locked.

Ana notes a faint smell of alcohol near the safe and summons Apoth trackers, led by Princeps Kitlan. The tracker confirms alcohol on the safe and, more importantly, detects Nusis’s blood on it, suggesting the safe was handled while bloody and then cleaned with alcohol. Ana has them corrode the hinges and remove the safe door.

Din inspects the contents and finds a “reagents key” present, but Din is certain it is not the same one Din retrieved from Aristan’s safe house: the bronze disc is discolored differently, lacks familiar dents, and feels the wrong weight. The tracker confirms the new key smells like an ordinary reagents key, heavily of blood, and also cleaned—implying tampering rather than untouched storage.

On the way back to the Iudex tower, Ana explains her conclusion: someone stole the original item from Nusis’s safe and replaced it with a convincing substitute key; then the twitch arrived, forced Nusis to open the safe, killed Nusis, and discovered they had been beaten to their prize. Ana reasons the twitch’s unusual cleaning of both safe exterior and interior is an attempt to hide what they came for, not routine caution after a successful theft. Ana further decides the original “reagents key” was likely not a key at all, but the mysterious “missing third” Din once overheard Fayazi Haza discussing.

Ana meets Iudex Vashta and claims there is a renewed threat against Fayazi Haza’s life and asks to summon Fayazi and Fayazi’s engraver to the Iudex tower at once, with maximum protection, as a leviathan’s approach will bring chaos. Afterward, Ana admits to Din she used the claimed threat as bait to draw Fayazi in, and says she now knows who the third poisoner is, how the ten Engineers died, what the “key” truly was, and where it is—yet she withholds details due to widespread corruption. Before entering her room, Ana orders Din never to open her door until Ana says it is safe, warning that tomorrow’s plan could either expose a murderer or get them all killed.