The elevator pitch for Steven Knight’s “Serenity” would be: “‘Key Largo” meets “Westworld.’” And it’s every bit as ridiculous as that sounds.

Seven decades after Humphrey Bogart indelibly steered a boat through stormy Atlantic seas, Matthew McConaughey has found his own tropical noir. But “Serenity,” one very leaky vessel indeed, has a strange, heightened atmosphere that goes well beyond the usual thickened air of film noir.

McConaughey’s Baker Dill is a fishing boat captain who, like Bogart was in “Key Largo,” is a veteran. He lives the life of an ornery and heavy-drinking bachelor on Plymouth Island, a small spit of unknown whereabouts (the film was shot in Mauritius) where there’s a single bar, the Rope, and everyone knows who’s sleeping with whom. (In Dill’s case, it’s Constance, played by Diane Lane.) He lives in a shipping container by the shore and when he strips naked to, as he announces, “take a shower,” he does a swan dive off the seaside cliff outside.

Maybe that’s about what you’d expect of a McConaughey movie set anywhere near a beach. But then strangely exaggerated metaphors begin popping up everywhere. Dill’s boat is named “Serenity” and he’s dubbed the elusive giant tuna he obsessively chases “Justice.” (That’s right. “Serenity” is about a fisherman hunting a tuna named Justice.) But why is he, for example, so pointedly drinking from a mug labeled “World’s Greatest Dad”? Why does he say things like “I’m a hooker without a hook”? And why on earth does some spilled water momentarily telepathically connect Dill to his young son who sits somewhere far away in front of a computer screen? Didn’t McConaughey get all his interdimensional parenting out of his system in “Interstellar”?

It turns out, there are answers to these peculiarities and others. A big reveal eventually washes ashore that both explains the film’s clumsy pseudo-reality and makes it only more absurd. You can’t say Knight, the talented screenwriter of “Eastern Promises” and “Dirty Pretty Things” and the writer-director of “Locke,” isn’t going for something audacious and grandiose here. “Serenity” isn’t the sort of misfire you are likely to quickly forget; its aim is too high and the results are too off balance. One tends to remember fish named Justice.

Whether a tamer film would have been better or worse is hard to say. On the plus side, there’s a blonde Anne Hathaway in full femme fatale mode, an occasion Knight celebrates with some of the most excitable camera moves you’ve ever seen. She plays Dill’s ex-wife who has tracked Dill, via Facebook, to Plymouth with the proposal that Dill take her abusive and alcoholic husband (Jason Clarke, a caricature of vileness) on a fishing trip and leave him at the bottom of the ocean in exchange for $10 million.

Certainly, Knight is more than capable of taking a simple if familiar genre set-up like that and turning it into something interesting. His “Locke” memorably made a terse thriller out of a plot that featured Tom Hardy alone in a car for nearly the film’s entire running time. But he has added a second layer of parable to “Serenity” that, without giving anything away, has something to do with that far-away boy and little to do with basic narrative structures.

“Serenity” may be hopelessly at sea but all of the performers are nevertheless fully committed to the tale, particularly Hathaway and McConaughey, who apparently has a thing for movies with boats (“Mud,” ”Fool’s Gold”). Both are led astray by a wayward script about a fisherman named Dill who’s caught in a bit of a pickle. “Serenity” now ? I wouldn’t recommend it.

“SERENITY”

* 1/2

(R, 1:46)