Simon Benford receives MARBLE’s encrypted burst transmission detailing the canary trap variants and Dominika’s assignment against Nate. He orders surveillance on Golov and the entire Russian Embassy to prevent meetings with SWAN. He and Nate spread the information about the shingles variant of Vanya’s trap within the US government in order to monitor whether it triggers a reaction from Moscow. Benford briefs the SSCI, where Senator Stephanie Boucher challenges him forcefully. He mentions that the suspected Russian penetration may suffer from shingles; Boucher and 14 other senators hear this.

In Moscow, Egorov and Zyuganov brief Korchnoi on the Nash operation. Zyuganov suggests harsher methods, but Egorov reveals that he has orders forbidding active measures against Nash—the operation will rely on Dominika seducing Nash to identify MARBLE. Korchnoi realizes Egorov is actively hunting him but feels confident he has not yet been specifically identified.

At his apartment, Korchnoi tests Dominika over a pasta dinner. He reveals that his wife died because the Russian embassy wouldn’t allow his wife to seek proper medical care, and that this hardened him against the regime. When he directly asks how the CIA recruited her, Dominika confesses that she chose to work with them on her own terms. He then tells her that the regime does not deserve their loyalty. Dominika realizes he is MARBLE, the mole Moscow is hunting.

Korchnoi and Dominika come up with a plan for Dominika to approach Nash in Rome. They brief Egorov and Zyuganov, and Zyuganov secretly makes his own arrangements, summoning Matorin.

The Washington rezidentura is stalled by weeks of FBI surveillance, but Rezident Golov must meet SWAN. Using a coordinated multi-car departure and a fishhook maneuver along Beach Drive, he breaks free and arrives at the Tabard Inn, where SWAN, Senator Stephanie Boucher, is waiting. Boucher reports hearing CIA briefings about a mole hunt targeting someone with shingles. She demands a pill to take in case she is caught, threatening to end their partnership otherwise. Golov promises to consult Moscow.

At a subsequent meeting, Golov presents Boucher with a Montblanc Etoile pen concealing a poison-coated needle for instant death. Boucher accepts it and passes him another disc from the aerospace contractor Pathfinder Corporation.

In Rome, Korchnoi and Dominika conduct extensive surveillance detection before meeting Benford and Nate in the Villa Borghese park. Korchnoi reviews his succession plan with Benford: Dominika will eventually expose him to preserve her position and continue his work from within the SVR. Benford protests, but Korchnoi insists the timing must be chosen carefully, and Dominika is the right successor. Benford notes that he used the shingles variant from the canary trap, and they both know Nasarenko will die.

Alone, Nate and Dominika discuss their relationship awkwardly. She tells him about her Lefortovo interrogation and how she survived by keeping his image in her mind. Rattled, Nate kisses her, and they have sex.

Matorin is also in Rome, waiting outside Dominika’s hotel for an operational opportunity.

The Orion surveillance team, a CIA unit of retired officers, studies Golov’s patterns and identifies his signature fishhook maneuver. Using their TrapDoor technique—anticipating a target’s destination rather than following directly—they position static posts along likely routes and track Golov to the Tabard Inn.

Benford calls the FBI immediately, but their deployment takes over two hours. By the time agents arrive, Senator Boucher has already met with Golov and departed unseen. Benford sharply criticizes the FBI for missing the opportunity. He demands that a CIA officer be present at any future arrest and designates Nate.

Egorov receives an urgent call from President Putin ordering that Dominika be sent to Athens for the Nash operation. Zyuganov begins making arrangements, tasking Matorin for the mission.

In Moscow, Korchnoi visits Nasarenko’s laboratory, sees him overwhelmed by discs awaiting analysis, and secretly pockets a Pathfinder disc that Nasarenko carelessly left on his desk. When Golov’s cable reporting that Boucher heard the shingles story reaches Moscow, Egorov and Zyuganov conclude that Nasarenko is the mole and have him arrested and brutally interrogated.

Sensing that the investigation is closing in, Korchnoi loads the stolen disc into a dead drop and transmits a burst message confirming the load. CIA Moscow Station retrieves the disc and couriers it to Washington. FBI forensics lifts three distinct fingerprints from the disc, and an automated database search returns an unexpected hit.

The fingerprints belong to Senator Stephanie Boucher. An FBI team arrives at Boucher’s California home with Nate and arrests her for espionage. Boucher reacts defiantly, instructing her assistant to call the attorney general and her lawyer, and refuses to answer questions. When Montgomery shows her a photograph of the disc bearing her fingerprints, she writes an obscenity rather than signing the confession document.

Boucher then pulls out her Montblanc pen, extracts the poison needle, and plunges it into her arm before Nate can stop her. The batrachotoxin causes massive convulsions, and she dies on the couch.

Egorov watches American news reports of Boucher’s death and realizes that SWAN has been lost. Reviewing Nasarenko’s interrogation tapes, he notices that Korchnoi visited Nasarenko, saw the discs, and offered to lend analysts. He begins to suspect his old friend may be the traitor, but the Athens operation against Nash is already underway, leaving him no time to pursue the lead.

In Athens, Dominika meets Nate in a Byzantine chapel after conducting surveillance detection. Over two days, they establish her cover story: She will report seducing him and that he is beginning to discuss his work. Meanwhile, Matorin is staying at a hotel adjacent to Dominika’s, where he sharpens his Khyber knife and prepares two auto-injector pens—one containing an interrogation drug, the other a lethal paralytic.

At Nate’s hotel, Dominika confronts him about their relationship, demanding he acknowledge their connection beyond operational necessity. After a tense exchange about whether they are lovers or merely case officer and asset, they have sex again.