Katherine Solomon shows Robert Langdon a classified Threshold binder and insists the artificial-neuron design is identical to what she described in her doctoral thesis twenty-three years earlier. She points to unique made-up terminology in the CIA document as proof it is not coincidence, and she explains that she had argued artificial neurons would need to be biological to integrate with the human brain.

Langdon presses how the CIA could have obtained her ideas, and Katherine begins to recall an odd episode from Princeton. While hurrying out with the binder to get it to the ambassador, Katherine recounts how her adviser, A. J. Cosgrove, believed her thesis deserved a major science prize and hinted she was denied for non-merit reasons; before she left neuroscience for noetics, he urged her to do something that now alarms her.

Katherine stops, realizing the implication: the CIA may have an even bigger reason to ensure her book disappears permanently. She tells Langdon that the new realization makes their situation more dangerous than she understood moments earlier.

Elsewhere inside Threshold, CIA officer Finch returns armed with Housemore’s SIG Sauer and moves through the facility after confirming multiple deaths. Having found Housemore’s corpse and then Gessner’s workroom, Finch confirms Brigita has been murdered as well and calls for backup, but expects delays and decides he must act immediately.

Finch notices a dropped metal epilepsy rod and concludes the intruder likely came from the epilepsy program, narrowing it to Sasha Vesna or Dmitri Sysevich, though Finch believes Dmitri is already dead. He doubts timid Sasha could have done it alone, but begins a systematic sweep of BIO and the surgical area, determined that anyone who has seen Threshold will not be allowed to leave alive.

Deep in the SMES vault, the Golěm climbs atop the humming machinery and reaches the crank that moves the test cover over the open quench ventilation shaft. Ignoring the red warning stenciled on the steel plate, the Golěm turns the handle to seal the vault, preparing to make the room airtight despite the protocol that it remain open.