Brad Pitt on a roll in Bullet Train

Bullet Train

Starring Brad Pitt, Joey King, Brian Tyree Henry, Aaron Taylor-Johnson, Sandra Bullock, Andrew Koji, Hiroyuki Sanada, Michael Shannon, Bad Bunny and Zazie Beetz. Directed by David Leitch. 126 minutes. Opens Friday in theatres everywhere, with Thursday previews. 14A

The first rule of “Bullet Train” is we don’t talk about the plot of “Bullet Train.”

If you insist, gentle readers, I suppose we could, messing with the silence code of “Fight Club,” which also starred Brad Pitt. But it wouldn’t do any of us a lick of good.

“Bullet Train” is a summer action vehicle where the gas pedal is fully depressed but the brain is set in neutral. Pitt plays a trouble-prone character who is like Bugs Bunny set loose in a speeding rail conveyance full of murderous Elmer Fudds.

This is more of a cartoon than a movie, directed by David Leitch, who specializes in style-over-substance confections like “Atomic Blonde,” the first “John Wick” and the second “Deadpool.” The screenplay by Zak Olkewicz is based on the Japanese novel “Maria Beetle” by Kōtarō Isaka.

What happens in “Bullet Train” means nothing. To whom it happens means a lot in terms of enjoying this brilliantly cast movie, at least until the story outstays its welcome.

The inimitable Mr. Pitt, who doesn’t get nearly enough credit for his comic timing and physical humour, hasn’t had this much fun since he played the mumbling thug in Guy Ritchie’s “Snatch,” one of the many blood-and-banter films that “Bullet Train” resembles.

Here Pitt sends up his superstar status by playing Ladybug, a flaky international spy and assassin in a bucket hat and black-rimmed glasses who is in the midst of re-evaluating his life.

Maybe, he reasons, there’s more to existence than doing “snatch and grab jobs” that invariably result in carnage resembling Grand Guignol theatre. Ladybug now wants to make the world a better place, refusing even to carry his trusty gun.

“You put peace out in the world, you get peace back,” he tells his cynical handler, Maria, played by a delightfully deadpan Sandra Bullock.

Can you tell he’s been doing meditation and reading self-help books?

Maria scoffs. She gave him the new code name “Ladybug,” a joke about his habit of being in the wrong place at the right time and leaving a scarlet puddle in his wake.

Hoping to ease him back into the espionage game, Maria gives Ladybug what looks like a no-brainer assignment: to recover a silver briefcase that’s aboard the world’s fastest train, zooming between Tokyo and Kyoto. (The briefcase is this film’s MacGuffin, a Hitchcockian device to prod action, as is a deadly snake that just happens to have been let loose on the train for added laughs.)

Neither Maria nor Ladybug reckon on him encountering the Looney Tunes assortment of troublemakers who are also on the train, literally along for the ride for the purpose of maximizing mayhem.

First and foremost are two engaging knuckleheads played by Brian Tyree Henry and Aaron Taylor-Johnson, who go by the names Lemon and Tangerine for the purpose of an eye-rolling running gag. They’re also known as “the Twins,” for an eye-rolling sight gag. (Leitch loves this kind of in-joke nuttiness: a furtive character reads the classic spy novel “Shibumi,” which was also spotted in “John Wick.”)

Lemon and Tangerine have their own designs on that silver briefcase, which they’re transporting to a very mean criminal kingpin known as White Death. Other homicidal characters aboard the train — played by Joey King (“The Princess”), Zazie Beetz (“Deadpool 2,” TV’s “Atlanta”) and the rapper Bad Bunny — have their own reasons for firing a gun, jabbing a needle or waving a knife around.

We learn that the bullet train everybody is aboard has 16 cars. It seems at times as if there are 16 different storylines, including an outrageous continuous product plug for Fuji bottled water.

The film often loses momentum, a weird thing to happen in a tale themed on propulsion. And for all the slapstick stoogery going on, the abundant killing isn’t hilarious and often way over the top. When Lemon and Tangerine argue about whether Lemon has killed 16 or 17 people, Leitch feels obliged to show us all of the hits, in one of the movie’s many rapid-fire montages.

The good news is that Pitt is in most of the stories and he clearly enjoys working under the watch of Leitch, a former stuntman who used to double for Pitt in films like “Fight Club” and “Ocean’s Eleven.”

Leitch can apparently persuade Pitt to do anything, including imitating John Travolta’s cocky walk in “Saturday Night Fever,” set to “Stayin’ Alive,” of course.

I wanted to like “Bullet Train” more than I did, but I liked it well enough as a summer distraction and Brad Pitt attraction to give it a pass. Peace out, as Ladybug would say.