There’s a lot of salesmanship that sits, obvious to the naked eye, in “Serenity.”

Here’s how “Serenity” was sold to overseas investors, and then to nascent studio Aviron, and how they in turn are selling it to us.

Matthew McConaughey skinny dipping, Anne Hathaway as a femme fatale, Oscar winners and “Interstellar” co-stars sharing sex scenes in a Virgin Islands (actually, Maritius in the Indian Ocean) setting.

Sell the all-star cast on a paid Mauritius working vacation. and voila, you’ve got yourself a movie.

It’s not much of a movie, an overboiled, rum-and-sex-soaked neo-noir about deep sea fishing, predestination and murder. And just as its not amounting to much, writer-director Steven Knight’s script (he wrote “Dirty Pretty Things” and “Locke”) takes a deep dive into flipping genres and reframing the narrative.

With plot contrivances piling up alongside McConaughey nude scenes, interrupted by moments where he tosses back his head and howls, Hathaway vamping up the ex lover who tries every argument in the book to talk this charter fishing boat captain into killing her brutish husband (Jason Clarke, perfectly vile), one is tempted to say that the only thing that worked here were the sales pitches.

McConaughey is Baker Dill, a hard-drinking hard-luck charter captain on tiny Plymouth Island, which has but one bar — The Rope and Anchor — and one cougar (Diane Lane) to keep him afloat. She loans him money after sex.

“You’re a hooker,” she cracks.

“A hooker who can’t afford his hooks,” he agrees.

His righteous, works-with-nuns first mate (“Amistad” co-star Djimon Hounsou) cannot cure Dill of his obsession, his Great White Whale. It’s a giant tuna he keeps hooking and never landing. “Justice” he calls it. He pulls a knife on two customers who try to take the rod and fight the fish onto the boat on THEIR charter in an opening scene.

“I fish tuna,” Dill growls.

“You fish for ONE tuna,” one and all agree. Everybody knows Dill’s story, knows who he sleeps with and the state of his finances because “Down here, everybody knows everything.”

They see the new blonde (Hathaway) who shows up, even if they don’t know Dill and Karen’s shared past. She’s got a proposition. Think “Palmetto” or “Body Heat.”

She uses their history. She shows a little leg and comes on to him. She plays the pity story, claims she’s being beaten. She wants her husband to go fishing, and not come back.

Dill is also being pursued by this mysterious nerd in a business suit (Jeremy Strong of “The Big Short” and “Detroit”). The guy keeps running down the dock, just seconds late in catching Dill, or taking off his expensive shoes to wade into the surf after him.

Weird.

The setting, the sexy tone, the cast and snippets of sharp dialogue tamped down my eye rolling through the film’s first half. McConaughey, who has mad more than his share of seaside tales, gives fair value in delivering salty lines.

“Who owns your boat?”

“Me’n the bank take TURNS.”

But it’s at that midpoint that Knight, an accomplished writer who let his director of photography talk him into a few too many pointlessly showy circle-the-character pans, takes a turn towards the desperate and turns his plot and his movie inside out.

Playing it as a straight noir wasn’t impressing anybody. Screenwriters and directors over 60 are have to try tricks to keep themselves relevant in a film industry driven by childishness.

But this twist popped whatever bubble of believability that makes “Serenity” watchable.

Still, you’ve got to hand it to any salesman who sold this cast, these producers and this studio on this project. Must have been a pitch for the ages, with “Mauritius” to seal the deal.

MPAA Rating: R for language throughout, sexual content, and some bloody images

Cast: Matthew McConaughey, Anne Hathaway, Diane Lane, Djimon Hounsou, Jason Clarke

Credits: Written and directed by Steven Knight An Aviron release.

Running time: 1:46