A single line — paraphrased by countless pornos but said verbatim at a key turn in “Strange Darling” — unlocks the heart of JT Mollner’s razor-sharp psychosexual thriller.

“I’ve never put it THERE before,” says someone in a scene that shouldn’t be described.

This horror movie is the best kept secret to come out of Fantastic Fest 2023. Until now, almost everything the public has heard about this magnificent slasher deconstruction was an intentional and ingenious misdirect. From its opaque title to its overly slick poster, this blood-soaked Trojan horse is rarely what you would expect. That’s true even and especially when it’s riffing on iconic tropes.

An excruciating chase film, a terrifying puzzle-box whodunit, and a testament to romanticizing even the darkest cinema in glowing 35mm, “Strange Darling” is an outright triumph. That much you can know now, although the following review treads very carefully to avoid spoilers.

Audiences going in with the least knowledge of what you could call a gut-wrenching date night will have the best crack at enjoying this movie in theaters — but there’s more than plot to recommend Magenta Light Studios’ jaw-dropping first feature. Yes, writer/director Mollner’s exacting script is a lean, mean vivisection of humanity’s never-ending hunt for a serial killer. Told nonlinearly, with chapter names signposting its story out of order, “Strange Darling” plays like an even more volatile “Pulp Fiction,” cocaine included.

But it’s also proof that actor Giovanni Ribisi has been hiding out as one of Hollywood’s greatest living cinematographers — a fact laid to bare in some of the most beautiful murders this side of Dario Argento’s “Deep Red.” The main cast further asserts themselves as top talent in the kaleidoscopic world of meta-performance. After a brief black-and-white vignette sets the stage with an instantaneous jump-scare, you’ll meet “The Lady” (Willa Fitzgerald) and “The Demon” (Kyle Gallner) in an opening sequence that feels ripped from the throat of “The Texas Chainsaw Massacre.”

Sprinting across an Oregon field in ruby-red scrubs — eyes wide like a deer, pallid skin bouncing in slow-motion — the enigmatic bleach blonde has crimson oozing from her ear. What happened there? The Lady is followed by a blitzkrieg in scarlet plaid, but we won’t see The Demon reach maximum fury until the high-octane car chase that follows. (It’s a brief but rip-roaring scene that might just make contemporary audiences understand why some of the earliest movie-goers once feared a train bursting through the big screen.) No, here The Lady is alone, credits in the foreground and the melodious “Love Hurts” floating somewhere overhead. It’s the first in an endless cascade of clashes designed for second-guessing.

The Demon might not catch up to her yet, but you’ll still feel the breath trapped in your throat as the seething actors and red-on-red shades emanate an angry delirium. Mollner begins his six-parter smack-dab in the middle with “CHAPTER 3: CAN YOU HELP ME? PLEASE?” but the filmmaker clues the audience in on a couple of other things before that. A tightly written crawl says the nightmare you’re about to witness is based on a true story (it’s not) and that it chronicles the last days of an especially sadistic murderer (that part is true…technically).

“Strange Darling” can do straightforward brutality with the best of them. And yet, throughout the film, the actors’ playful portrayal — dipping in and out of an ever-shifting dynamic that seems too complicated to write down, let alone embody — recalls something like Mia Goth’s dazzling performance in “Pearl.” Fitzgerald tests her endurance in some delicately drawn-out one-shots, while Gallner makes his bid for small-time scream king armed with a shotgun and an assuredness that feels like its own assault. Comparisons between “Strange Darling” and most other modern horror movies should stop there, if only because the timelessness these singular characters capture can make even great genre efforts look trite.

Before saying anything of his nightmarish story, Mollner makes a point of including another slate: “SHOT ENTIRELY ON 35MM FILM.” That self-indulgent choice in a horror movie might make some cinephiles scoff, but Ribisi earns the recognition. This isn’t Mollner’s first rodeo — the writer/director made “Outlaws and Angels” before this — and he knows what he’s got. As the tension builds past what even the characters can take, their director wants your eyes open enough to admire what his director of photography has achieved. The lighting and relighting of a single wig in this film deserves its own featurette.

Editor Christopher Bell proves equally essential, assertively reorienting audience perspective with an almost comic relentlessness. Bell’s scalpel-like cuts are meant to screw with your head. That may prove too challenging for some viewers, who will already be high on a supply of arresting violence and original tracks by alt-rock musician Z-Berg. And yet, the dreamy core of “Strange Darling” will push real genre fans forward — finding revelatory relief in comedy so black it could make even a non-smoker want a cigarette.

When The Lady encounters an older couple living in an idyllic cabin in the woods, Barbara Hershey and Ed Begley Jr. complete the cast. She’ll struggle to decide if they’re friend or foe, but it’s the rock-solid actors’ relationship with each other that will be talked about when “Strange Darling” is in the rearview. Genevieve and Frederick are introduced in a scene that silently shows them making breakfast. Jam. Syrup. Sausages. Pancakes. Four sticks of butter… with whipped cream on top?! Their intimacy — built on the back of a gross-out recipe that could only be discovered by people who are totally and alarmingly in love — gifts Hershey what may prove to be the best acting beat of her career.

Electric and unforgettable, “Strange Darling” lives up to its maddening moniker. In a summer movie season that’s been middling at best, this is a must-see — a feat of filmmaking so extraordinary you’ll wonder if it could ever truly be spoiled. You’ve met this man and this woman. You know these tropes and their horrors. But in this exceptionally slippery film, somehow never once losing its traction, you’ve never seen “it” put “THERE” before.

Grade: A

From Miramax, Spooky Pictures, and Magenta Light Studios, “Strange Darling” is in theaters August 23.

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