Langdon stops an SUV on a windy ridge above Folimanka Park and approaches Crucifix Bastion with Katherine, betting his plan will either save them or doom them. Replaying earlier events, Langdon reasons that Everett Finch’s sudden order to secure the bastion, combined with the CIA-run surveillance “blind spot” around Brigita Gessner’s lab and the building’s perfect overlook of Threshold, suggests the bastion is more than a cover institute.

Langdon explains his suspicion: medieval bastions often had a poterne, a hidden “back door,” and a modern version could be a vertical shaft or elevator descending toward the bomb-shelter complex beneath Folimanka Park. He concludes Q’s purchase of the bastion for Gessner was likely meant to provide Threshold with an additional, discreet access point masked as the Gessner Institute.

Inside, Katherine is stunned by the bastion’s lavish, gallery-like atrium and senses the luxury is camouflage for something darker. Langdon goes straight to a welded metal wall sculpture, shoves it aside, and reveals an elevator alcove; he also notices a couch that is slightly out of place, suggesting someone has been here since his earlier visit.

At the elevator, Langdon points out two access systems: a keypad for Gessner’s private lab one floor down and an RFID reader that would likely authorize deeper descent to Threshold. He enters the passcode he previously solved, and they ride down to a corridor of rock walls and modern lighting, passing office space, an MRI lab, and a door marked with a VR-goggles icon.

As they near the workroom where Gessner’s corpse lies, Langdon admits he dreads seeing the body again; Katherine tries to steady him by framing corpses as empty shells and describing near-death research that portrays death as a relief from the body. Langdon hurries to Gessner’s briefcase for the needed RFID card, but finds the lock shattered and the latches pried open; the contents are mostly intact except the key card, which is missing.

Katherine reveals the worse implication: the card would not have helped anyway because it is biometric. She points to bloody wire cutters near the EPR pod and concludes that whoever stole Gessner’s access card also took Gessner’s thumb to use her fingerprint.