In a boiler room beneath Petschek Villa, Ambassador Heide Nagel explains that she knows few specifics about the CIA’s “Threshold” project because the agency keeps her “insulated.” She says the CIA director considers Threshold the agency’s most important endeavor, and that three years earlier the CIA engineered her embassy posting so she could act as a diplomatic facilitator answering to Everett Finch.

Nagel believes Threshold is a heavily secured subterranean science facility tied to Brigita Gessner’s technologies and likely focused on brain research or human consciousness. Although the structure is complete, it is not fully operational; Nagel says limited testing has been successful, staff are training off-site in the United States, and the facility is expected to go live within weeks.

Nagel reveals Threshold is located beneath Prague in the abandoned, deeper sections of the Soviet-era Folimanka Shelter under Folimanka Park. She describes how the U.S. Army Corps of Engineers publicly “helped” the city address fears the park was sagging, while secretly draining, sealing, reinforcing, and rebuilding the larger, forgotten bunker network for CIA use. When Langdon asks why build in Prague rather than the U.S., Nagel says dense urban settings camouflage activity from satellites and foreign locations reduce congressional oversight and domestic legal restrictions.

Pressed on why she is helping, Nagel admits her motives are personal and warns that in Threshold’s orbit “people die.” She reports that Michael Harris, her legal attaché, has just been found dead in Sasha Vesna’s apartment; Nagel says Harris was surveilling Sasha via a relationship ordered by Finch, and Sasha is now missing. Nagel takes responsibility for having followed Finch’s orders and vows to protect Robert Langdon and Katherine Solomon.

Nagel offers three options: (1) sign new nondisclosure agreements and meet Finch, securing safety at the cost of Katherine’s freedom and publication; (2) flee to the airport immediately, buying time but with major repercussions and little practical ability to publish quickly; or (3) let Finch believe the NDAs were signed, extract as much information as possible during the meeting, and use it as leverage via an “untimely death clause” held by a third party so the information goes to the press if they are harmed. Langdon doubts Finch will reveal enough, then declares there is a dangerous “fourth option” he believes may be best.