“Years and Years,” created by Russell T. Davies, as a joint production of the BBC and HBO, might best be described as dystopian realism. A messy, audacious blend of a Jason Katims family drama, like “Parenthood,” and a tense political thriller, in the tradition of “24,” the series is set in a horrifying potential version of right now—which is to say, it opens shortly before Donald Trump is reëlected. By the end of the first episode, a nuclear bomb has gone off near China. The world should end, but it doesn’t—and that same trauma recurs again and again. In the course of six episodes, “Years and Years” keeps leaping forward, forcing us into the future, as the economy crumbles, the ice caps melt, authoritarianism rises, and teen-agers implant phones into their hands. It’s an alarmist series, in a literal sense: it’s meant to serve as an alarm, an alert to what’s going on in front of our eyes, and where that might lead, if we don’t wake up.

The characters struggling to respond to these frightening developments are the Lyonses, a Manchester-based family that seems designed to represent every demographic in a pollster’s pie chart: cross-class, cross-ethnicity, cross-sexuality. Anne Reid plays the comfortable white boomer Muriel, whose large suburban home becomes a refuge for her family when the financial systems buckle. Her grandchildren are Stephen, a rich white banker in London who’s married to Celeste, a black accountant, with whom he has two teen-age daughters; Rosie, a white working-class single mother with spina bifida, one of whose children is half Chinese and trans, the other behaviorally troubled; and the affectionate Daniel, a housing officer who leaves his husband for Viktor, a Ukrainian refugee and a resident of the facility that he oversees. The fourth Lyons, Edith, is a globe-trotting anarchist activist, who, in the first episode, witnesses that bomb go off, as her family follows along on TV. When she comes home, she’s sick with radiation poisoning and seemingly burned out on politics. Her fate feels like a metaphor for the world’s: It’s all going to end, but when? And is it too late to fix things?

There’s a lot of plot for six episodes. As a result, the Lyonses don’t always feel fully real, especially during scenes in which they all Skype together while watching TV, shooting observations back and forth as if they were on a CNN panel. The dialogue veers from wry humor (“Ah, the missing sister. Aren’t you supposed to be dying?”) to Sorkinian speechifying. During more syrupy bits, I began to think of the show as “This Is UK.” And yet this mild artificiality winds up serving the show’s purposes. We care about the Lyonses (about Stephen losing his money; about Rosie’s love life; about Muriel’s great-granddaughter Bethany, who, in the show’s most fascinating plotline, saves up money for surgery to become a cyborg), but there’s just enough aesthetic alienation that we observe their struggles from a distance. They’re less like people than like lenses we put on—to experience the seething resentment, say, of a former banker scraping by in the gig economy, irritated to have to expend his empathy on outsiders.

What grounds the series is a classic love story: the bond between Daniel (the always wonderful Russell Tovey) and Viktor (Maxim Baldry), a taboo attraction that deepens into something lasting. Their affair starts with Viktor cruising Daniel—he shows him the scar on his foot, from being tortured. It becomes a story of patience and devotion as touching as that of Ruth and Naomi in the Bible. Davies, who created the original “Queer as Folk” but is now best known for the relaunch of “Doctor Who,” has made a specialty of treating gay characters as a hinge of history, and some of the most skillful aspects of “Years and Years,” including its time jumps, reminded me of his show “Cucumber,” which in one episode traced the path of a gay man’s entire life, from his childhood to his coming out to his violent death. Davies gives Daniel and Viktor’s story a similar heartbreaking clarity.

The other truly effective plot is the story of Bethany, played with nuance and tenderness by Lydia West. Bethany begins as a depressed teen-ager who hides behind Snapchat-like virtual masks. Her parents suspect that she’s trans—but, in fact, she tells them that she’s “transhuman.” This sounds outlandish, but it makes dramatic sense onscreen, as Bethany grows up to be an intelligent young person who makes a strong case for a sort of “maturity” outside the realm of modern imagination. What should be horrifying—a lurid “Black Mirror” nightmare—is rendered both comprehensible and complex.

The show’s real horror story is something far more familiar. In the first episode, a charismatic provocateur emerges on TV—a gleaming-toothed Emma Thompson, playing a faux-feminist Trumpette, Vivienne Rook, whose calling card is saying rude things on talk shows, in a familiar “I’m just saying what everyone thinks!” vein. When the Lyonses first see Rook’s act, they all laugh. But, step by step, her brand of fascism gets Trojan-horsed into viral celebrity. A couple of Lyonses even start to support her, craving someone to shake things up, almost as if they were hoping for a plot twist. “That’s Vivienne Rook,” the far-left Edith says. “She’s ripping up democracy. I love it.”

The Lyonses are not the only aggressively diverse TV family of the past few years. Such portraits have become a go-to narrative tool for a range of purposes, on shows from Freeform’s heartwarming “The Fosters” to HBO’s sludgy “Here and Now” (a more self-serious drama made in response to Trump’s rise). You could trace the emergence of this phenomenon to the pilot of “Modern Family,” in which the big revelation was that seemingly unconnected people were family members, or maybe even to the proto-family that made up “Lost.” Some of the reasons for this are pragmatic: a diverse family is a shortcut to diverse casting. It’s also a natural metaphor for a nation, a way of making it logical for people who might otherwise not meet to bicker over dinner. In “Years and Years,” the device is used to inject emotion into the political thriller that unspools in the final two episodes, as—spoilers follow—the Lyonses begin to unite to expose Rook’s nastiest schemes.

It’s a twist that feels less than satisfying, after so much earned cynicism. And, in fact, by the time that the final episodes air in the U.S., certain world events in the series—the emergence of concentration camps for immigrants, especially—will have been outpaced by reality. In “Years and Years,” the population revolts when it witnesses the mistreatment of “disappeared” refugees. Rook’s exposure leads to legal consequences—and the Internet helps out, too, in spreading the word. The series softens, unable to acknowledge another possibility: that people might be shocked, once again, then shrug and do nothing. As shows often do in their finales, the series finds closure but sells out its ruder and more challenging ideas in the process.

A central refrain of the show is “What happens next?” That’s what people ask when something is confusing or frightening or exciting. There’s a meta quality to the phrase: “What happens next?” is also the mark of a cliffhanger, of all serialized TV drama, what keeps us watching. Here, it’s used to indicate a modern state of overload, when what’s happening begins to seem so outrageous that it’s as though we were living in a simulation—which is to say, inside our own action show. When everything is a crisis, nothing is. Late in the series, Muriel is offered a miracle: she can cure her encroaching blindness by using advances in stem-cell therapy, but if she takes the deal she’ll leave no money to her descendants. This situation might strike American viewers as fairly ordinary, since going bankrupt in a medical emergency is par for the course here. In Britain, it must seem more apocalyptic. In any case, Muriel doesn’t hesitate. She accepts the bargain, like any binge watcher: “It’s a terrible, terrible world, but I want to see every second of it.” ♦