We all know what a MacGuffin is (and in case you don’t, here’s what it is): an object or event that the plot of a thriller hinges on, and which everyone onscreen keeps talking about, yet it has no intrinsic interest apart from how it serves the structure of the movie. The term was mythologized by Hitchcock, and as shorthand for the way a certain kind of movie works it has never gone out of style. But what do you call a MacGuffin that’s so boring the audience can’t pretend to care about it? Let’s call it a MacMuffin.

“Heart of Stone,” a double-crossing espionage thriller that is joyless, convoluted, and sludgy-looking — in short, abysmal — is a movie chockful of MacMuffins. Gal Gadot, working hard to come off as blithe and cool (something one should never work hard to do), plays Rachel Stone, an intelligence operative who is part of a chummy veteran spy team that works for Britain’s MI6. She’s the group’s token geek, a tech wizard who never goes out in the field.

Except that as we learn, that’s all a ruse. Rachel is a counteragent, a spy among spies. She’s actually a member of the Charter, an international group of agents who have bonded together — with allegiance to no country — to make the world a safer place. We see her interact with other members of the Charter, yet the outfit is really the film’s first MacMuffin. We never have any idea of what they’re up to, how they operate, or where they fit into the global nexus. They’re just a utilitarian thriller abstraction.

Rachel isn’t the only member of her MI6 team who’s fooling everyone. So is Parker (Jamie Dornan), a charmer who flirts with Rachel — but that’s mostly an act, since he’s got his own agenda. It revolves around trying to get his hands on the Heart, an all-powerful device of artificial intelligence that sounds a lot like the Entity, the Internet-gone-amok villain of “Mission: Impossible — Dead Reckoning Part One.” The Heart, which has been in the hands of the Charter, is “Heart of Stone’s” second MacMuffin: a concept that’s theoretically fun to think about (and that looks, when we see it, like the world’s most complicated espresso maker), yet we never actually witness it doing anything. It feels like a virtual threat orchestrated by a virtual screenwriter.

There are many reasons why movies are now too long, but “Heart of Stone,” which clocks in at a laborious two hours, demonstrates an especially wearying form of bloat. With Gadot’s Rachel as a superspy out to save the world, the movie is a degraded descendant of the Bond thrillers. Yet it doesn’t have a plot so much as an endless digressive chain of events that are churned out like sausage links. This isn’t storytelling, it’s wheel-spinning. The movie could just as well have been four hours long: Here’s one more overblown set piece! One more hollow twist for your excitement! The director, Tom Harper (who made the very good “Wild Rose”), keeps the action pumping — the hand-to-hand fights and machine-gun battles, a cardboard 007 prelude in which Rachel manipulates her way through a casino, then parachutes down the side of a seemingly endless mountain. And there’s a parade of global locations that amounts to a weather collage: the desert of Senegal, Iceland, European cities that get turned into ornate backdrops of destruction.

Rachel, for all her imperviousness, emerges from that opening sequence seriously shaken-if-not-stirred by the presence of Keya, a mysterious hacker who cast a meaningful glance her way in the casino. Who is Keya? She’s the film’s third MacMuffin: a character we’re supposed to pretend to be invested in, but all we can think is that the actor, Alia Bhatt, comes off as too courtly and innocent to compete with the lethal chicanery around her.

Gal Gadot is game, but there’s a slightly downbeat earnestness about her that doesn’t mesh with the reflexive quippiness of the dialogue. Dornan proves he’s got what it takes to be debonair and conniving at the same time, yet the closer we get to Parker’s plan the smaller it seems. That’s the way a MacMuffin works: Pay it much scrutiny, and it collapses on contact. What makes “Heart of Stone” such an enervating experience isn’t that it’s incompetent but that nothing in it matters. It’s all bombast and noise, all hollow logistics, all virtual “Minority Report” screens and clattering fury signifying nothing. In other words: Time to start planning the sequel.