Although the better part of the new episode of FX’s The Americans fourth season focuses on Elizabeth (Keri Russell) and Philip (Matthew Rhys) quarantined in Gabriel’s (Frank Langella) apartment, the most interesting segments occur on the sidelines. The tedium of the Glanders complication is only enhanced by the fact that all the unspoken rules of TV — even if in our more adventurous, shock-value-filled day and age — tell the viewer that neither Philip, Elizabeth, or even Gabriel will die. And ultimately, they actually come out of the Glanders crisis totally unscarred — just slightly closer to another, and after some feverish deliberation, on the same page about sparing the lives of Pastor Tim (Kelly AuCoin) and Alice.

But what truly resonates in “Chloramphenicol” are moments like Martha’s (Alison Wright) emotional phone message to “Clark,” and when Stan (Noah Emmerich), searching Martha’s apartment while Dennis Aderholt (Brandon J. Dirden) wines and dines her, finds evidence that she is hiding a significant other. What this leads him to conclude is unclear — but we’re led to believe that he sees the possibility that there is a motivator behind the scenes. The most crucial advance in the longer-term plot, which one risks forgetting by the end of the episode, comes when Henry (Keidrich Sellati) lets slip to Stan that his parents have been “traveling a lot.” The flicker of suspicion on Stan’s face — and again, when he presses Paige (Holly Taylor) further about it — makes for the most thrilling moments of the season so far.

Of course, this promising setup for bigger and better developments is not meant to be the main attraction in the episode. The seismic moment occurs in the final moment of the episode: when Nina (Annet Mahendru) is shot unceremoniously in the back of the head, for charges of treason she has been doing her best to evade for a long time. An eerie energy in earlier scenes related to her in the episode make it clear that something bad will likely happen to her soon (The only source of doubt: Why keep her on the show to dispose of her this way?). The deal Oleg (Costa Ronin) makes with his father on her behalf seems too vague, and definitely too good to be true — a literal “get out of jail” free card. Her final dreamlike vision of Stan, Oleg, and Anton (Michael Aronov)— full of shining, ethereal light — makes her fate clear beyond a shadow of a doubt.

In some overarching way though, Nina was on her way out of the show for a long time. In prison, she had her own micro-plotlines, but they were amorphous. There was always the sense that we were just biding our time with her until she could be reunited with other members of the core cast. Her scenes with Anton are non-directional, taking us closer to understand her inner life rather than advancing the storyline. But they were important, in the sense that when Nina was functioning as a double agent before her deportation, and even before, she was the show’s most inscrutable and morally ambiguous character. She became less opaque during her time in prison. So what is powerful about Nina’s death is that we look at her face in closeup, dead on the ground, we feel like we finally know who she is, and have come to terms with her. Her trajectory in prison was toward being comfortable with who she was and realizing her insignificance in the eyes of the governments whose dirty work she had done — perhaps, in the world at large. By the end, she was ready for this moment.

So while the loss of Annet Mahendru’s talent is saddening, this brutal conclusion for Nina is logical, and even something of a relief. We had already found closure with her character; it was simply the exact timing and methodology of the kill that was surprising here. With Nina’s departure, there is more room in The Americans for the real battles to begin for our core cast. But still, we’ll miss her a great deal.

Photos via Jessica Miglio/FX