In the fifth-season finale of “The Americans,” Elizabeth Jennings (Keri Russell), a covert Soviet agent in the United States, offered some advice to a young Vietnamese counterpart: Get a partner. “You’re not going to make it,” she warned him. “It’s too hard, the work we do, to do it alone.”

Now, Elizabeth is doing it alone.

At the outset of the sixth and final season, which begins Wednesday on FX, three years have passed since Elizabeth’s husband and collaborator, Philip (Matthew Rhys), burned out and left the spy game.

Their cover — suburban Virginia parents running a travel agency — has become his real life. While he books international tours, she’s fomenting the international revolution, alone and wearily, and the strain is showing.

“The Americans” has always been as much or more about marriage and partnership as about geopolitics. In fall 1987, as the drama picks back up with a strong trio of opening episodes, the two are colliding, with a little hope and a great deal of dread.

It is the end of so many things. The end of the Reagan era is coming, with government officials worrying privately that the president is starting to go senile. The ends of the Cold War and the Soviet Union are in the offing. Could this also be the end of the Jenningses’ marriage?

That “The Americans” makes you care about the answer without excusing the characters is its great accomplishment. It doesn’t sugarcoat that Elizabeth and Philip are in an ugly line of work and do unforgivable things. They kill civilians, lie to their kids, ruin lives.

But unlike other bad-guy cable protagonists, they do it out of principle, however misguided. Elizabeth believes passionately in socialism. Philip’s politics are shakier, his loyalties more personal. They’re soldiers, recruited at a young age in Russia for an arranged marriage that over the years became a real one.

Philip’s bowing out has left them distanced. He’s always been more at home in America than she has. Now he’s all-in, giving motivational speeches about salesmanship and taking up country line dancing. She’s overworked and overstressed, juggling multiple covert operations.

The divide in their relationship parallels the one back at home, where the reformer Mikhail Gorbachev is being resisted by hard-liners in the KGB, who pull Elizabeth into a plot to undermine an arms summit meeting in Washington. She can tell Philip about none of this. Glasnost may be stirring in Russia, but an Iron Curtain is descending in their home.

It’s a jarring development in a series that’s been a story of marriage as equal partnership. In the season premiere, when Elizabeth bitingly cuts off Philip’s attempt to get her to open up about work — “I know you love to talk,” she says, dismissively — it’s as breathtaking as any act of violence in the series.

Where the previous season dragged, this one opens with a sense of things closing in. The first few hours suggest any number of ways things can end in heartbreak: for Oleg (Costa Ronin), a principled former KGB agent who supports the reforms; for the Jenningses’ FBI agent friend Stan Beeman (Noah Emmerich), who’s unwittingly been on their trail for years; for their son, Henry (Keidrich Sellati), happily oblivious to his family’s origins.

That’s true above all for their idealistic daughter, Paige (Holly Taylor), now in college, whom Elizabeth has been easing into the spy life. As nerve-racking as it is to watch, “The Americans” makes Elizabeth’s decision understandable from her perspective: If you believe this is a battle for the future of every child, how can you exempt your own?

Espionage, it turns out, is a great bonding experience. Paige and Elizabeth spend hours with Claudia (Margo Martindale), Elizabeth’s handler, watching the Soviet movie melodrama “Moscow Does Not Believe in Tears” and cooking up a batch of zharkoye, a Russian peasant stew. Elizabeth reminisces to Paige about her own mother making giant pots of it to fend off starvation.

Elizabeth is committed to Marxism as an idea, yes, but she’s fighting for more than an abstraction. Her nation is not just an ideology. It’s meat scraps and potatoes. It’s memory, taste, a history of shared privation and loss — an ancestral call that survives the rise and fall of regimes. All of this rings especially strong in 2018, when we know well that the end of the USSR was not the end of history or of nationalism.

It’s that melancholy intimacy that makes “The Americans” more than the sum of its wigs, stabbings and spot-on period-music choices. (No plot point in “The Americans” is as big a spoiler as its soundtrack selections, so I’ll keep them to myself.)

The history itself is no spoiler; we know how the Cold War played out. But “The Americans” understands history as more than the record of which nations rise and fall. It’s also the story of individual people for whom life goes on, or doesn’t.