An over-the-top, violent and campy prologue sets us up for the all-star action romp that is “Argylle,” an espionage comedy from the fellow who unleashed the “Kingsman” franchise, Matthew Vaughn.

Brawls and epic shoot-outs break out, droll action heroes and venemous villains smirk and sneer, bodies fly about and the body count soars in a light thriller that begins with great promise and stumbles into ponderous “streaming” pacing before the struggle to rally at the finale arrives.

Sam Rockwell and Henry Cavill shine, Bryan Cranston fumes, Catherine O’Hara kvetches and Sofia Boutella meets her bombshell vixen match in the screen debut of sexy singer Dua Lipa in a tale that almost intentionally makes little sense, and can’t make much use at all out of genre icons Samuel L. Jackson and John Cena.

But I am hard-pressed to think of another movie that literally comes to a complete halt the moment its co-star makes her bow. There’s no getting around the deer-in-headlights bust that Bryce Dallas Howard is — a miscast, unemotive and dull dead weight on a picture that can ill-afford to stop and take stock of how messy it is.

Howard, of the recent “Jurassic” reboot, may look the part of the timid, mousy novelist whose thriller series about an agent named “Argylle” (Cavill) is her way of living vicariously through her wildly popular fiction. I kept thinking of Mormon Mom Stephenie Meyer, author of the “Twilight” series.

But director Vaughn has her do public readings from her books, and writer Elly Conway’s beaming “I’m a hit” smile can’t hide flat recitations of flat prose that sounds like plot summaries cut-and-pasted into an Amazon ad and a question and answer session cringily bad, one that goes on and on until we’ve almost forgotten the over-the-top spectacle of the opening gambit, featuring Cavill and Cena and Dua Lipa shooting and vamping their way through a Greek getaway scene dreamed up by our writer-heroine.

Vaughn saddles nepo baby Howard — daughter of Ron — with an often-digital cat which she tries to dote on, but which none of the spies who try to grab her or the spy who tries to protect her (Rockwell) treats with shall we say “the same affection.”

And while she can’t shoulder all the blame for the bust “Argylle” turns out to be, her leaden turn in the leading role points out how clunky the rest of this Pan European spy vs. spy saga becomes for its long, drawn-out middle acts

Elly Conway is trying to finish her latest book, and please her fiercest critic — her mom (O’Hara) — when her train ride is interrupted by a supremely scruffy and smart-alecky spy (Rockwell) and a sea of would-be assassins.

Turns out, her latest book — unfinished and thus still-unpublished — has “kicked a hornet’s nest” in the spy world. Agent Aidan, whom Elly can’t help but hallucinate her dashing hero Argylle onto as he busts up the train and every bad guy on it before affecting her “rescue,” might be trustworthy. Or he might not.

“Isn’t this fun?” Aidan cracks, and we’d agree. The action beats in Vaughn pictures generally are, with grand choreography and cinematography and digital tricks hiding the stuntwork.

But as the plot thickens, it curdles. As the “Your fantastic imagination is the key” to a spy scandal, treachery and international wrong-doing grows more dependent on Howard’s Elly, out of her depth but expected to pitch-in on the mayhem, “Argylle” grinds to a halt.

Vaughn, who has never quite shed his “Guy Ritchie Lite” label, builds big fight scenes around dance and disco music, with Barry White kicking off the festivities right from the start.

But White’s iconic-to-the-point-of-cliche “We got it together, didn’t we?” lyrics mislead. “Argylle,” which bounces from a Colorado Amtrak ride to London, France, Saudi Arabia and the deep blue sea, mixing real settings with digitally-augmented ones, real actors doing real action with stunt-folk and CGI de-aging and a digital cat, is more a jumble of jaunty, glib set-pieces than a narrative he ever gets his arms around.

The sight gags work, almost to a one, with Cena grabbing Lupa’s villainess off a moving motorcycle a comical highlight. Stone-faced Cavill almost seems to be having fun. Not as much fun as the dancing, death-dealing Rockwell, who is in fine form, but enough to hint at the James Bond Cavill might have become.

But “Argylle” — note the spelling — is about as fun as a box of socks for Christmas, plaid, checkered or argyle.

Rating: PG-13, action violence, innuendo, profanity

Cast: Sam Rockwell, Bryce Dallas Howard, Henry Cavill, Bryan Cranston, Catherine O’Hara, Sofia Boutella, Dua Lipa and Samuel L. Jackson.

Credits: Directed by Matthew Vaughn, scripted by Jason Fuchs. A Universal release.

Running time: 2:19