What a delightful little French-flavored English bon bon this is.

“Sleeping Car to Trieste” may be a corny, old-fashioned “Orient Express” rail-bound thriller, peppered with intrigues both deadly and quaintly silly. But by the time this sleeper hits the third act, it’s chortling along, leaving us unprepared for the laughs and a shocking jolt as a punchline.

The formula was already so tried and true by 1948 that viewers then and now don’t need to know it’s a remake of “Rome Express” (1932) to know how this goes. But when it gets up to speed, my how it “goes.”

A cunning, socially-connected “agent” of some sort (Albert Lieven) breaks into an embassy in Paris, steals a book and shoots a man who sees him do it. It’s only when we meet Zurta’s confederate Valya (Jean Kent) that we realize “the information in that book” “means revolution,” should it get out.

But they are double-crossed by a middle man, Karl (Alan Wheatley), who absconds with the book and onto the Orient Express, bound for Zagred and someone who pay a higher price for this book, “revolution” be damned.

There’s nothing for it but for the duo to board the train themselves, hunt him down and retrieve “the book.”

Married lawyer George (Derrick De Marney) is also traveling, with Joan (Rona Anderson), who is not his wife, something they go to extremes to conceal. That problem is made far more difficult when George’s boorish old classmate Tom (oft-employed character actor David Tomlinson) turns up.

There are sisters trying to avoid “declaring” purchases to customs, availing themselves of a skirt-chasing American GI (Bonar Colleano) to hide their contraband, who finds himself sharing a berth with a bird-watching bore (Michael Elvin).

By coincidence, a famous florid, solicitous French policeman (Paul Dupuis of “Passport to Pimlico”) is taking this trip as well. And then a famous political scientist and writer (the venerable Finlay Currie) checks in, with his secretary (Hugh Burden).

That’s a full complement for chef Poirier (Coco Aslan) to feed. If only this English blowhard (David Hutcheson) wasn’t job-shadowing him for the trip.

The first acts are all about Karl, aka “Poole” trying to get a berth all to himself and avoid being seen, George and Joan trying to share a berth despite Tom’s insensate berth-blocking and our agents Vayla and Zurta trying to get their hands on Karl, “the book,” or both.

Veteran director John Paddy Carstairs, the son of an actor, brother of a producer and director of comedies and thrillers with a comic touch (“Trouble in Store”) all the way into the TV era (“The Saint”) ensures that this train gets out of the station in a timely manner, and that the lighter touches all land.

The pompous Brits are set against the eye-rolling French at every turn, especially in the well-mannered put-downs of Detective Inspector Jolif.

“Tell me, can an Englishman even ‘sin’ with honesty?”

Dupuis is a stand-out in the cast, with Tomlinson at his irritating best and Currie harrumphing his way through his scenes.

The infidelity business isn’t played for laughs, and even the changing mores haven’t added amusement to that part of the story. There’s a laugh or two in American actor Colleano’s embodiment of British notions of every Yank “over there” during the war and after it — over-sexed and gauche.

“Really mee-shurrrr,” a French lass has to tell him. “I don’WAN to be ‘leeberated’ any more!”

‘Sleeping Car to Trieste” is light entertainment, nothing more. But even if the action scenes (fights) lack a lot, even if it takes a while to get up to speed, the production design, lovely matte painting backdrops, card-game standoffs and the like make this trip back to an era, a place and the sorts of movies that came out of it worth your time.

Rating: approved

Cast: Jean Kent, Albert Lieven, Paul Dupuis, Finlay Currie, David Tomlinson, Rona Anderson, Derrick De Marney, Bonar Colleano and Grégoire Aslan

Credits: Directed by John Paddy Carstairs, scripted by Allan MacKinnon, based the Clifford Grey script to “Rome Express.” A Two Cities/J. Arthur Rank release on Tubi, Amazon, etc.

Running time: 1:35