The pitch has a hint of “madcap” about it.

A teenage spitfire and future rebellious movie starlet goes to New York at 16, accompanied by an older and over-matched chaperone.

But even though “The Chaperone” is coming to theaters, it’s a PBS/Masterpiece Films production. PBS doesn’t do madcap. Nor does esteemed screenwriter Julian Fellowes, of “Downton Abbey” and such films as “Shadowlands” and “Gosford Park.”

What “Masterpiece Theatre” does well is “starchy” and “soapy,” and that’s what this melodrama, “inspired by true events,” manages. It’s a handsomely-mounted, pleasant but dry and almost dull trip back to the Roaring 20s, “Masterpiece” style. Which is it say “Roaring” isn’t really allowed.

The “Downton” connection is underlined by parking Elizabeth McGovern in the lead role. She is Norma, a Wichita housewife who overhears a conversation at a charity benefit and offers to act as chaperone for the talented and vivacious 16 year-old Louise Brooks, played by the effervescent Haley Lu Richardson (“Five Feet Apart,””Split”).

Norma’s husband (Campbell Scott) has no say in the matter, which practically shouts “FORESHADOWING!”

“I hope you won’t go…digging around, when you get there,” is all he says in protest.

And Louise is sell hell-bent on getting out of Wichita that she’ll say anything that placates her indulgent but mistrusting parents (Victoria Hill, Jonathan Walker).

It’s the Prohibition Era, the Jazz Age. And Brooks, with just a hint of the bangs that would anchor her iconic much-copied “bob” when she became the quintessential “flapper,” and a star of such films “A Girl in Every Port,” Pandora’s Box” and “Miss Europe,” is desperate to, as the poet put it, “gather” her “rosebuds” in the big city.

“I don’t intend to live the way I was brought up,” the cocksure dance student declares to Norma. She eschews corsets and is straining at the leash to flirt, drink and romance her way into New York.

“I never worry about anything!” Especially men willing to buy her this or that. Whatever it costs them, “They get the pleasure of my company.”

She’s been accepted at the modernist Denishawn dance school and company, which the real Brooks actually joined — though in Los Angeles, not in New York.

Norma? She’s cautious and provincial. “I have not come here to harass you. I am here to protect you.”

She’s there to put the brakes on whenever Louise, who came to be known as “Lulu,” kind of the first “modern woman,” is about to get out of hand. “It isn’t done…because of the appearance of impropriety.”

And sex?

“Men don’t like candy that’s been…unwrapped,” dear. “They don’t know where it’s been!”

Louise cackles at that. “We’re not all like Marmee in ‘Little Women’ you know.”

But that’s as far as that conflict is developed, really. “The Chaperone” is about the title character’s journey. Norma’s “digging around” is about her past. She was an orphan, from back in the days when nuns ran orphanages and children were loaded onto trained to be adopted out to who knows who in the far reaches of America. Norma wants to know who her birth mother was.

There’s a helpful caretaker (Géza Röhrig ) at the orphanage where Norma wants to get some answers.

The dizzy “Miss Pettigrew Lives for a Day” direction this film might have taken might be light and trite, even. But Louise Brooks is a fascinating figure, and Richardson — seen dancing quite capably in that “Rite of Spring” era style — might have the spark to make that work.

What Fellowes elected to show us instead was a drab melodrama with a few big emotional moments where McGovern gets to show us some fireworks.

Fellowes does his homework and like many a TV screenwriter, “shows his work”  with carefully placed historical references to “speak easies” and the “I support Prohibition!” climate of the time.

“Did I tell you? Jack and I are joining the Klan!”

“What clan?”

“The Ku Klux Klan!” a Wichita friend chirps to Norma, complaining about the social changes that have come “since the war” — “laws, customs, morals…Everything’s falling apart!”

Louise and Norma experience their first integrated theater audience (the show is meant to be 1922’s “Shuffle Along.”).

There are revelations — each woman has a painful secret or three — love interests, all rather pallid ingredients to a formula that plays better on Fellowes’ famous Anglo-American PBS soap opera.

The scenes that delight are often in the dance studio, where wife Ruth St. Denis (Miranda Otto) and Ted “Papa” Shawn (Robert Fairchild) lecture their students on dance, movement and propriety — which Louise isn’t hearing.

“”From this moment, you are ambassadors…for DENISHAWN!  No drinking or smoking…wear hats and stockings and NEVER roll down (your) stockings!”

Otto, still best known for her ferocious youthful turn in the “Lord of the Rings” movies, is imperious and almost funny — the embodiment of the pretentious artiste.

“Art is not tinsel. It is gold. And it must be handled by the worthy…DAHNCE is…a visualization of divinity!”

It’s pointless to wish for more of this, because that’s not what Fellowes does well. But those flashes of fun might have given the great screenwriter an unsettling moment or two in the editing.

He had to realize he was telling the wrong story, a duller one by design, even if it does star his beloved Lady Grantham.

MPAA Rating: unrated, adult situations, alcohol abuse, mild profanity

Cast: Elizabeth McGovern, Haley Lu Richardson, Miranda Otto, Campbell Scott, Blythe Danner,

Credits:Directed by Michael Engler, script by Julian Fellowes, based on the Laura Moriarty book. A PBS/Masterpiece Films release.

Running time: 1:43