Nothing rankles the people quite like a bad mom, a depiction so offensive that most movies take the side door. Maternal malevolence is no rarity in the history of cinema, as the filmographies of Alfred Hitchcock and Ari Aster will readily attest, but it’s often relegated to the sidelines, propelling stories without fully seizing their reigns. When occasionally offered the spotlight, malignant motherhood is uniformly couched in comedy, softening the blow with broad jokes and climactic changes of heart, lest our preconceived notions of saintliness be challenged in any meaningful way. The invisible halo is implied and assumed, an angelic signifier that doubles as a glowing boundary, a gentle reminder of lines that are not to be crossed. Having hit pause on an up-and-coming career to parent her own small child, writer/director Mary Bronstein has had nearly two decades to stew on the societal parameters of her situation, watching her male contemporaries be lauded for their big screen achievements while being inundated with dimensionless portraits of feminine grace and sacrifice. Some anger’s been a’brewin,’ enough to put purity and virtue on the back burner. Today’s the day to throw a toaster in the bathtub.

But only if you have the strength to lift that tiny appliance, and Linda (Rose Byrne) is just about out of gas. With her husband on an extended work trip, she’s been using every ounce of energy to look after the couple’s ailing young daughter, shepherding her progeny to endless doctor’s visits while tube-feeding her throughout largely sleepless nights. That doesn’t leave much in the tank for her job as a therapist, struggling to keep her eyes open while being waylaid by unexamined sob stories, an imbalanced back-and-forth that’s flipped on its head whenever she takes a turn on her unnamed coworker’s couch. It’s enough to make you punch a hole through the wall, but the plumbing in their Montauk apartment has got that covered, sending a cascade of water falling through the ceiling, and forcing Linda and child to relocate to a shady hotel complex. What should be a simple patch job is besieged by delays, but when it comes to property damage, the call is coming from inside the house.

You have to get close to hear it, but Christopher Messina has got you covered in that respect. Training his lens on Byrne with no regard for personal space, the cinematographer wriggles his way into Linda’s headspace by means of relentless proximity, capturing Byrne in sweaty, disheveled close-ups that drown out everything beyond our protagonist’s immediate purview. Count the kiddo amongst the casualties; despite being voiced by Delaney Quinn, Linda’s charge is only heard, never seen, a simple cosmetic choice that elucidates Bronstein’s aims with a simple tilt the camera. Tales of pipsqueaks in mortal danger are a dime a dozen, vacuuming up audience sympathy and rendering their caretakers as an afterthought. Legs is so determined to center Linda that it doesn’t even give you an option, confronting its viewers with the unexplored trauma of being a supporting cast member in your own life. Bronstein, who wrote the script during an analogous period in her own life, isn’t about to let that suffering fall on deaf ears, following Byrne’s every movement, no matter how ugly.

Rest assured, it gets grisly, but Byrne is quite the captain amidst a choppy sea. Brilliantly leveraging the goodwill and sympathy she’s built up over years of comedies, the Australian actress practically dares you to look away, taunting the viewer with feral screams, persistent alcohol abuse, and too many midnight jaunts away from her daughter’s bedside to count. Arguing over a fictional character’s basic morality is bargain bin criticism, but Legs would surely lose its audience with a less talented performer, a regrettable potential that Byrne stymies through conviction and brute force. She’s a marvel, believable and haunting in every frame, underselling the movie’s dark humor with the delicacy of a brain surgeon when she’s not busy taking a blow torch to the online cottage industry of morality mongering.

Not that you should see her for professional help, though that’s true of just about everyone in Legs’ rogue’s gallery of flailing assistance. Playing out like an extended airing of grievances, Bronstein mines vocational ineptitude for all it’s worth, and constantly finds gold in the trenches. No one takes that ceiling rupture seriously, the desk attendants at the new digs are better at rolling their eyes than selling their goods, and all forms of medical advice are administered with a healthy dose of condensation, most gratingly by Bronstein herself, who plays a nurse with an aversion to niceties. Even the guinea pig that Linda’s kid so desperately covets can’t perform the duties of a loving pet, its eventual fate representing the movie’s most riotous punchline. It’s not alone as far as knee-slappers go, and one of Legs’ most impressive attributes is the way in which its black-hearted jests serve dual purposes, empathizing with a person who’s lost faith in those around her while slightly deescalating the flick’s near-hazardous sense of tension.

Without them, the whole enterprise risks sinking into its own harried, hard won despair, offering surprise and solace to a flick with a determined downhill trajectory. Bronstein can clearly hear doom’s beck and call, a dimly-lit worldview that calls Safdie brothers hits Good Time and Uncut Gems to mind, a connection bolstered by Josh Safdie’s producer’s credit. Sharing that latter flick’s interest in the metaphysical, Legs finds room for a few psychedelic free falls into the subconscious that are juicy and ambiguous enough to be puzzled over for years, occasionally making their intentions clear while leaving other exposures tantalizingly vague. The plight of Caroline (Danielle Macdonald), a client of Linda’s who’s struggling under a heavy blanket of postpartum depression, is decidedly more earthbound, but no less elusive and thought-provoking in its execution, adding an air of ruminative mystery to a film that’s already fully accomplished in the field of rousing nihilism.

There’s enough rage here to push just about any viewer to the brink, an accolade that Bronstein safe guards from implosion through some of the best stunt casting you’ll ever see. Picking up where his charismatic turn in Highest 2 Lowest left off, A$AP Rocky is making quite the career out of being a scene stealing embodiment of charm; his follow hotel dweller isn’t asked to do much beyond enlivening the proceedings, but he’s a magnet for corneas. Same goes for Conan O’Brian as Linda’s aforementioned therapist, playing into his testy off-stage reputation by deliciously draining his line readings of anything but latent scorn. The potential for distraction is real, but they’re both outstanding, taking a little weight off of the ball-and-chain that ever threatens to stop the film dead in its tracks. Assigning the ally label to anyone receiving both pay and exposure for their efforts is mostly fool-hardy, but there’s no question that Legs’ modest box office performance received a big boost from their unexpected presence. In truth, the movie might never have seen the light of day without their names on the dotted lines.

Such are the trials of selling any movie concerning a debased woman, let alone a mother. Even with Bronstein’s absolute diamond of screenplay, financiers were slow to bite, their trepidation seemingly justified by the dearth of recognizable comparison points. Maggie Gyllenhaal’s arresting Netflix drama The Lost Daughter comes to mind, as does Jason Reitman’s criminally underrated Young Adult, though neither are a hand-in-glove fit. If I Had Legs I’d Kick You is on its own tortured, hilarious, maddening wavelength, a deftly layered and singular testament to Bronstein’s importance in an industry that’s starving for original voices. Her’s sings in a register that’s only foreign to cinephiles; myriad mothers know the tune from lived experience, and the movie’s climactic visual metaphor is no less powerful for its immediate legibility. Those ocean waves, promising solace and oblivion before retracting their offer, don’t see Linda for who she truly is, but Bronstein does, and she’d like to show you.