While Liz chases a Russian spy hired by the cabal to execute an act of domestic terrorism, her search for her mother's past makes her a target.
It's early morning on a college campus when a grad student bumps into an older gentleman we'll call Andropov, who's handing out anti-Patriot Act literature. After bonding over their political beliefs, the student signs Andropov's petition, shakes his hand and continues on his way... until he starts spasming uncontrollably and bleeding from the eyes. As he hits the ground, Andropov makes a call, saying, "We've achieved customization. Initiate Phase 2."
Across town, Liz finds Tom sitting alone in a diner. Their conversation is a riddle to us and likely to the both of them: Tom apologizes, something he should have done a long time ago - though he's not asking for forgiveness. He's hopeful that his dream scenario can finally begin: Liz will join him on his boat, sail off into the sunset, maybe they'll even get naked at some point. Liz is incredulous - she doesn't know Tom at all - which is when her favorite breakfast plate arrives, pre-ordered by Tom. Tom admits his dreamboat scenario isn't realistic, but they both need to start over, so why not together? Liz could start by calling him Jacob... Of course, that's when Red calls, summoning Liz to Caul's house. After Liz tells Red that she's going to learn the truth about her parents on the night of the fire despite his silence, he lays out the next Blacklister: the cabal has smuggled Karakurt, aka the Left Hand of the SVR, into the U.S. to commit an act of terrorism on a defense installation. Since it will look like the Russians did it, the Feds will blame Moscow, thus setting up another cold war. The stakes are urgent: Karakurt must be stopped.
Liz presents the case on Karakurt to the Task Force, explaining Red may have a lead. Unwilling to wait, Cooper sets up a meeting for Liz and Ressler with the CIA's Office of Russian and European Analysis at the OREA Building. They're met by assistant Marshall Masik, who warns them his team leader, Matt Kilpatrick, is a tough nut. Indeed, Kilpatrick is argumentative, unwilling to reveal his sources and doesn't believe Karakurt is on U.S. soil. Nevertheless, he wants the Russian spy more than anyone and promises to follow up. Masik runs after Liz and Ressler to beg forgiveness. Kilpatrick has an old-guard ex-pat CI, a local restaurant owner, who recorded a conversation last night that might be helpful. Masik hands over a flash drive, and Liz shows him the photo of her mother - has Masik heard of Katarina Rostova? Masik doubts the veracity of the photo, since Katarina Rostova is known in intelligence circles as a myth, the subject of tall tales. Nevertheless, if Liz will send him a copy of the photo, Masik promises to ask Kilpatrick's CI.
Red finally comes up with an address for Karakurt, so he and Dembe proceed to the filthy apartment where they find bomb-making chemicals and a nosy neighbor, a young mother with a colicky baby. Posing as private detective Bill Houston, Red asks the mother to call the next time she sees Karakurt... which helps her remember that she saw him in a van in the alley. Liz is just filling Ressler in on the search for her mother when Samar calls with a location on the van: it's parked right outside the OREA building! Liz spies the van just before it explodes, destroying the building she and Ressler just exited and sending them flying.
The Task Force huddles around monitors at the Post Office, watching news coverage of the explosion, which left no survivors and is now framed as a terrorist attack by Senator Clifford Hawkins. Red calls Liz to ask where they are with Karakurt, raising her ire. They're nowhere! The cabal put a bullet in Red's chest and just wiped out an entire CIA substation! Across town, the young mother spies Karakurt entering the filthy apartment, so she calls Red, who in turn, calls Liz with the address. Liz and Ressler head out just as a highly annoyed Connolly arrives, demanding that Cooper ignore Red's tip and divert his team to Union Station... or Charlene will pay the price. Cooper complies, so Liz and Ressler proceed to the station, armed with a grainy photo of a guy in a grey hoodie and orange vest. Liz chases a likely suspect who knocks her down and knocks her out, then disappears into the crowd.
Back at the Post Office, Aram has downloaded a recorded conversation between two Russians from Masik's flash drive. A voice we know to be Andropov's says, "The proof of concept succeeded as projected. Prepare to initiate Phase 2." Then the other guy says, "We've identified the markers for targeting and customization." Samar believes she knows the identity of Kilpatrick's CI: Anton Velov owns a restaurant named Ninoshka's where virologist Dr. Leo Andropov paid for a dinner for two last night. It's not long before the FBI raids Andropov's abandoned lab to find evidence that he may be creating a biological weapon with the intention of starting some type of pandemic.
Cooper tells Red all about Connolly's blackmail plot. Sympathetic, Red advises Cooper to keep a stiff upper lip and continue to follow Connolly's orders without question - which will give them a chance to find out what the cabal is up to. Liz interrupts with a request. They're going to need an expert in microbiology who can read Russian to decode Andropov's notebooks. Of course, Red knows just such a person, so he brings Liz to meet flirty cougar Dr. Lauren Kimberly. While waiting for results, Liz ignores a call from Tom, who leaves a nervous message as Jacob, an attempt to start their relationship over with a dinner invitation for tomorrow. Moments later, Lauren has decoded Andropov's notes: he's synthesizing a fast-acting rotavirus designed to kill one specific individual. In the car, Liz and Red talk through their clues... until Liz figures that someone attending the memorial service for the dead CIA agents at St. Agnes Church is Karakurt and Andropov's ultimate target.
Liz and Ressler share their grainy photo of Karakurt with Metro's head of security outside the church, while Aram struggles to reverse engineer the virus against a DNA database to identify its victim. With no time to complete this task, Cooper decides they'll move forward with the assumption that Karakurt has infected himself and is the live carrier for the virus, which is communicable by touch and incapacitates its victim in seconds. Liz and Ressler return to the church, where the memorial service is about to begin, while Red and Caul muse over next steps. Thinking Andropov must have performed a trial, Red has Aram search local ERs for a recent patient with symptoms consistent with the effects of the virus. Aram identifies Connor Jennings, the student from the opening scene, and Samar discovers that he's the illegitimate son of none other than Senator Hawkins. At the church, Liz and Ressler keep their eyes peeled for Hawkins, while Red asks Cooper to tell Connolly they've identified Karakurt's intended victim - maybe he'll be caught off guard and call off the attack? Nope, he won't - and no one's aware that Karakurt is already at the church, posing as a journalist and tracking Hawkins, who's just arrived. But something Connolly says makes Cooper call Liz, ordering her to look for a journalist. Spying Karakurt just as he's about to shake hands with Hawkins, Liz intervenes, whisking Hawkins into Ressler's SUV. Unfortunately, only a few moments elapse before Hawkins starts convulsing and bleeding from his eyes... So, since he didn't touch Karakurt, who infected Senator Hawkins?
Karakurt is taken into custody as Hawkins remains in critical condition. Liz girds her loins, preparing to interrogate Karakurt as Tom sits alone at a restaurant, waiting. Back at Caul's house, Red pours a glass of nalivka for a frightened Anton Velov. Since the CIA agents Velov was working with are dead, Red hopes the man will now work for him. Velov mentions he got a call from Liz about Katarina Rostova - whom he didn't know personally - oh, and there were a couple of guys from the Justice Department who paid him a visit. They wanted to know about Katarina's child... Alarmed, Red orders Dembe to fetch his phone on the double. Back at the Post Office, Aram interrupts the interrogation to tell Ressler that Karakurt's blood tested negative for the virus, just as Liz's phone rings. Red tells her to leave now - she's been set up! The cabal has established a chain of evidence to make her look like a Russian spy, just like her mother. Red knows Liz will test positive for the virus, making it look like she infected Senator Hawkins. They're coming for her... And indeed, Connolly and his armed guards are prowling the halls of the Post Office...