The marvellous new espionage thriller “Black Bag” is, among other things, a sparkling ode to a happy marriage. I’m referring, in part, to the union between the movie’s central characters, George Woodhouse (Michael Fassbender) and Kathryn St. Jean (Cate Blanchett), top-ranking British intelligence agents who happen to be longtime spouses. But I’m also describing the thriving creative partnership between the director Steven Soderbergh and the screenwriter David Koepp—two prolific Hollywood veterans, both in their early sixties, who have found in each other a nimble and industrious kindred spirit. Both Soderbergh and Koepp understand the mechanics of genre inside out; they also know that those mechanics, given a proper greasing and a burst of inspiration, can still yield richly pleasurable dividends.

They’ve made three thrillers together over the past three years, and every one of them hums with wit, style, and low-key formal ingenuity. Their first, “Kimi” (2022), was a no-frills neo-Hitchcockian exercise about an I.T. analyst with a covid-exacerbated case of agoraphobia; it played like a pandemic-era “Parallax View” or “Rear Window” with browser windows. Next came “Presence” (2024), an extraordinarily inventive haunted-house movie that transformed a camera into a spectral observer—a ghost in the machine. Both films were home-invasion thrillers for a digitally paranoid age, and both projected, in different ways, an ambivalent fascination with the growing reach of contemporary surveillance technology: an Alexa-style virtual assistant in “Kimi,” a handheld recording device in “Presence.”

Although conspicuously slicker and starrier than its two immediate predecessors, “Black Bag” is also about a home invasion of sorts. (The precise nature of the break-in, including the means, the motive, and the culprits’ identities, is kept largely under wraps until a doozy of a final scene.) Surveillance, meanwhile, comes with the territory: all six of the movie’s main characters are employed by Britain’s National Cyber Security Centre and thus are essentially professional voyeurs. “I can feel when you’re watching me,” Kathryn purrs to her husband one evening, aware of his eyes upon her as she dresses for dinner. George is, indeed, a very good watcher; he’s known to be such a ruthless master of spycraft that he once surveilled, and coldly exposed, his own cheating father. Confronted with this unpleasant memory, George simply replies, “I don’t like liars”—a line that Fassbender delivers with an icy impassivity reminiscent of the most famous George in literary espionage: John le Carré’s George Smiley, as chilly in affect as he was prodigious in skill.

Unlike Smiley, however, George Woodhouse is not married to a serial adulterer. He and Kathryn appear to be as improbable a picture of romantic stability as you could find in a profession that demands extreme, around-the-clock duplicity. George and Kathryn don’t compromise, they compartmentalize: “black bag” is a shorthand they’ve evolved for ultra-classified intel too sensitive to share with each other. But, of course, because “black bag” is an all-purpose alibi, it’s also the perfect cover for a spy planning to betray spouse or country alike. As the story opens, George is tasked by an N.C.S.C. higher-up (Gustaf Skarsgård) with tracking down just such a traitor. There’s a mole in the organization’s midst, and a deadly cyber-MacGuffin, a weapon called Severus, is in danger of falling into the wrong hands. And so George sets out to catch the mole in his own inimitable, faintly sadistic style: he invites four colleagues, all of them suspects, to a dinner party at his and Kathryn’s fabulous London flat. There, under dim amber lighting, George laces the food with lip-loosening drugs and waits for the mole to drop a clue.

In a slyly kinky twist, the guest list consists of two other couples, which makes the inevitable dinner-party shenanigans play a bit like James Bond by way of Edward Albee—call it “Who’s Afraid of Virginia W007f?” There is Zoe (Naomie Harris), who, as a staff psychiatrist, has access to almost everyone’s secrets, and her boyfriend, James (Regé-Jean Page), an ambitious colonel who is also one of her patients—an arrangement that seems untenable on many levels. The other two invitees are an even more volatile duo: Clarissa (Marisa Abela), a young data expert, turns quickly and violently exasperated with her lover, Freddie, a cynical older agent known for drinking and screwing to excess. Freddie is played, wonderfully, by Tom Burke; after his roles in the film “The Souvenir” and the detective series “Strike,” he clearly has no peer in boozy irascibility.

Some devious fun and games ensue and promptly backfire. Sexual patterns and proclivities are mocked, personal indiscretions are laid bare, and there follows a spectacle of viciously eloquent backbiting—and, in one case, bloodletting. All of which curious George, a dab hand at psychological manipulation, coaxes along with the gentlest of nudges. He and his wife observe the fallout with a certain analytical detachment, although you can detect, in both Fassbender’s and Blanchett’s beautiful poker faces, a sliver of personal amusement—a cat-that-ate-the-canary smugness. It isn’t just that George and Kathryn are potentially trapping a traitor; it’s that they’re dealing with colleagues whose personal lives are the definition of a hot mess, and who make their model of coupledom look all the more enviable by comparison.

Why, then, do we detect a tremor of unease beneath the cool, comfortable surface of George and Kathryn’s marriage? Perhaps because Fassbender and Blanchett can flood even a passing glance with glimmers of complication and nuance—or perhaps because the one thing George doesn’t tell Kathryn is that she, too, is on his list of suspects, and he is surveilling her along with their guests. He had instructed her, before dinner, to avoid the chana masala; it takes a beat to realize that we, like Kathryn, have only George’s word for it. Maybe he spiked the wine instead.

The casting of Naomie Harris, the most recent incarnation of Moneypenny, isn’t the movie’s sole tip of the trilby to James Bond. A gray and glowering Pierce Brosnan turns up partway through as a peevish agency head, skulking behind translucent boardroom glass. It’s as if Agent 007, having been rudely kicked upstairs, is now determined to make life miserable for the next generation in the field. And yet there is only a soupçon of globe-trotting intrigue here, and barely enough mayhem to qualify “Black Bag” as an action movie, though what little there is has been staged with elegance and poise. Soderbergh and Koepp work swiftly and precisely, never repeating a trick. They grant us exactly one disturbingly enigmatic murder sequence; one meticulously staged car explosion; one nail-biter of a secret assignation, set in picturesque Zurich; and one lethal gunshot, signalling the story’s climax with clean, Chekhovian finality.

If the physical action is doled out in parsimonious bites, the verbal action is an extravagant feast of double helpings. Apart from two sequences where all six major characters gather under George and Kathryn’s roof, nearly every crucial scene takes the form of a pas de deux, springloaded with nearly indistinguishable secrets and lies. When James drops some unwelcome intel during a fishing trip with George, it’s hard to tell exactly who’s baiting whom; when Kathryn has a mandatory therapy session with Zoe—an interaction that Blanchett and Harris play with diamond-hard brilliance—you can practically see and hear each woman trying to get inside the other’s head. There’s a playful and almost promiscuous energy to the way Koepp keeps pairing his characters off, in new and surprising configurations, and the actors all rise to the challenge with astonishing dexterity. The most scintillating exchanges take place between George and Clarissa, whom Abela, last seen crooning up a storm as Amy Winehouse in “Back to Black” (no relation), invests with an irresistible spark of naughtiness. Clarissa may have the singularly unsexy job title of “data scraper”—as if data were barnacles, to be painstakingly raked off the gargantuan hull of the internet—but she emerges, in Abela’s sly and suggestive performance, as the movie’s most wickedly uninhibited mind.

It’s George and Kathryn, of course, who compel the most attention as their relationship comes under threat, and whether that threat comes from without or within is the film’s most pressing and emotionally loaded mystery. (That the much-coveted weapon is called Severus may be a reference to ancient Rome, but, if you split the word in two, you may find a lurking warning about the menace Severus poses to the happy couple.) As Kathryn acknowledges at one point, her and George’s marriage is often regarded as a professional weakness—a liability that could fatally compromise them both. Without revealing too much, “Black Bag” gives the lie to that assumption; monogamous commitment, it suggests, has its place even in a world as treacherous as this one.

If that sounds incongruously optimistic, it is nonetheless in keeping with the understated moralism—and the unfashionable rejection of cynicism—that has become a crucial thematic foundation of Soderbergh and Koepp’s work. “Kimi,” for all its digital booby traps, was ultimately about a frightened shut-in mustering the courage to bring a killer to justice. “Presence” was about a ghost doing everything in its power to save another person’s life; its explicitly Catholic underpinnings, as my colleague Richard Brody noted recently, speak insistently to the notion “that higher powers are at work in human lives.” “Black Bag,” for all its worldly intrigue, has unexpected Christian interventions of its own; one character’s unexpected yet unswerving spiritual convictions figure into the plot. Soderbergh and Koepp, for their part, express their own fervent belief: in the seductive glamour of espionage and the magnetism of Blanchett’s and Fassbender’s interlocking gazes—which is to say, in the enveloping artifice and power of movies. Great is their faithfulness indeed. ♦