Describing “Saltburn” in cinema shorthand terms is so easy it almost gives away the game. Not that the plot is any big inscrutable secret.

It’s “The Talented Mr. Ripley” meets “Call Me By Your Name” — insidious, class conscious, with a bit of violence and a serious taste of the sexually kinky if not downright icky.

The latest feature from actress turned “Promising Young Woman” writer-director-to-watch Emerald Fennell is a slap-in-the-face assault on British classism and an uninhibited tour de force for star Barry Keoghan.

Taken at its dark-intended-as-darkly-funny face value, it’s a satire that crosses lines simply because they’re there and easily overstays its welcome. But it’s still a bracing depiction of ancient fault lines breached by an interloper which the inbred and posh are ill-equipped to reckon with.

The Irish actor Keoghan, last seen in “The Banshees of Inisherin,” is a hapless “scholarship boy” at Oxford, “Class of 2006.” He’s as out of place as his trying-too-hard, dated “Oxford” fashions, as helpless as the look on his face every time he asks “This seat taken?” at his college’s wood-paneled, chandeliered, ancient and venerated dining hall.

That may relegate him to sitting with the highly-strung, self-described “genius” Jake (Will Gibson) as a fellow outcast in this world. But we know from Oliver Quick’s voice-over narration that he aspires to greater things, chief among them the rakish, handsome and ever-so-rich Felix Catton, given a louche ease and comfort about the “station” he was born into by Jacob Elordi (Elvis in “Priscilla,” TV’s “Euphoria”.

A chance encounter leads to a Oliver doing a boon for his rich, entitled classmate. And it doesn’t matter than Felix is related to Oliver’s trying-too-hard-at-snobbery tutoring partner and nemesis Farleigh (Archie Madekwe of “Midsommer” and “Gran Turismo”). “Ollie” soon finds himself sharing pints at the pub, palling around with the effortlessly popular girl magnet Felix and ingratiating himself into his life.

Little details about Ollie’s hard luck life story seem to touch Felix, who is rich enough to be gallant about picking up a tab without sweating it, and touchy enough to not like being reminded of it.

“Get yourself a title and a massive ‘f–k-off castle,” and you don’t have to hear how “only rich people can afford to be filthy” and never clean their college dorm room.

“Saltburn” is the family’s “castle,” a massive, Tudor manor house “pile.” Oliver finds himself invited there over summer break, instantly out of place as he takes an earlier train, goes through multiple gates and crosses vast grounds to get to the towering front door, where butler Duncan (Pauls Rhys) is quietly disapproving of his arrival.

He’s not the only one. The venmous Farleigh is here for a long stay.

Felix’s nonchalant attitutude about this wealth and status is summed up on a long walking “tour” through ornately-decorated halls and rooms covered with portraits — “Dead relly (relative), dead relly, Shakepeare’s Folio…Henry VIII…” But we sense a kindness in him as well.

He may make “Ollie” a subject of gossip with his parents (Rosamund Pike, terrific, Richard E. Grant, spot-on), his strikingly beautiful sister (Alison Oliver) and ever-over-dresssed ne’er do well houseguest (Carey Mulligan). But that’s only to urge them to mimic his consideration to his classmate.

Farleigh won’t buy in. Duncan keeps an eyebrow raised. But that’s not an issue, and it becomes obvious that Ollie is an “innocent” among a wading pool-deep cadre of upper class twits and their seldom-challenged progeny and hangers’ on.

“I have a complete and utter horror of ugliness, ever since I was young,” trophy wife matriarch Elspeth (Pike) declares.

Titled patriarch Sir James (Grant) gushes over every film they watch on movie nights — “Superbad” among them.

And daughter Venetia (Oliver) is a rareified creature of rebellious tastes and eating disorders, who might just have something in mind to do with the peasant boy now in their midst.

But Ollie’s early warning system should be triggered when she refers to him as not quite the same as “last year’s ‘one,” And maybe the Cattons and their hangers-on should have their guard up to this unpolished, seemingly-roughcut lad who can’t quite fit in, but who seems like too quick a study to be underestimated.

Mulligan, Grant and Pike are the reliable laughs in this cast, hitting just the right “clueless” touch here, a spectacularly tone-deaf touch there.

Fennell’s wit includes from lightly mocking the champagne swigging swells who play tennis in evening wear, bottle in hand, who nude sunbathe on the grounds — the younger generation snorting coke and the older one “planning” parties for their huge staff to actually pull-off, many of them just too polite to cope with modern mores or anyone who overstays their welcome.

Keoghan, one of the most accomplished actors of his generation (“Dunkirk,””’71,” “The Killing of a Sacred Deer,” “American Animals,” TV’s “Chernobyl”), impresses early on and turns downright dazzling in the later acts, accepting every challenge from a director prone to “Let’s just GO there” whims in this follow-up to the more focused and furious “Promising Young Woman.”

There hasn’t been much more to be said about upper class twits, filthy rich fussbudgets and entitled folk too polite and sheltered to perceive a threat in years, and Fennell doesn’t really change that.

And that “overstays its welcome” jab suits this picture to a T, as our clever filmmaker decides to linger past drop-the-mike moment and then over-explain it all in a draggy finale.

It’s the film’s sexual “daring” and its calculated shocks that stick with you more than the guessable narrative populated by assorted predators and prey.

But Keoghan — as innocent or cunning, oaf or graceful dancer-in-the-near-dark, will leave you amazed at this performance and startled at just what he was willing to do to fit in in “Saltburn” — the great house or the not-quite-great movie.

Rating: R, violence, drug abuse, “graphic nudity,” profanity and “strong sexual content

Cast: Barry Keoghan, Jacob Elordi, Alison Oliver, Archie Madekwe, Carey Mulligan, Paul Rhys, Richard E. Grant and Rosamund Pike.

Credits: Scripted and directed by Emerald Fennell. An MGM/Amazon Studios release.

Running time: 2:11