Both Sides of the Blade is the third straight collaboration between Claire Denis and Juliette Binoche, following the loose, relatively minor Let the Sunshine In and the darkly bewitching High Life. In fact, this pugilistic drama about flagrant infidelity is a kind of Denis repertory get-together: filling out its love triangle are Vincent Lindon, the Mitchum-esque star of Friday Night and Bastards, and Grégoire Colin, the brooding Billy Budd of Beau travail, who reappeared as a love interest in 35 Shots of Rum. There’s even a cameo for Mati Diop, who debuted opposite Colin in the latter film before becoming a redoubtable filmmaker in her own right.

Shooting during lockdown with this ensemble perhaps helped Denis cut to the chase – or the bitter core of her material, a scenario co-written with the French novelist Christine Angot. The film sets out its stall with a shimmering prologue set on holiday: Sara (Binoche) and Jean (Vincent), who’ve been together 10 years, swim off the coast somewhere and have passionate sex in their hotel. The music seems to serenade their happiness with a lyrical piano theme, but there’s something else: a low cello note that’s the first thing we hear, which persists beneath as an ominous bedrock.

Instability is the order of the day. Sara’s apparent contentment is ripped away the second she claps eyes on her ex François (Colin), an erstwhile best friend and business partner of Jean’s. His return after a long absence, and proposal to employ Jean as a rugby coach, are dangerous triggers for bed-hopping of the time-honoured French kind.

We know Sara’s predicament not from what Binoche is given to say, but from body language that gives her away like crazy. When she’s caught off-guard by spotting François on a motorbike, she physically reels from the shock, and has an extraordinary gesture in a lift afterwards, kneading her guts as she whispers his name. At work as a radio presenter, she goes through the motions, but her mind is clearly elsewhere. Soon relentlessly interrogating Jean about all François’s comings and goings, she’s stepping up to an affair so unsubtle even Madame Bovary would be impressed.

The rest of the film is 80 per cent spousal combat, with curiously few scenes of the affair itself. It peaks before it’s even begun, at the very moment when Sara and François are properly reintroduced – like a chemical reaction in dizzy close-up, with Tindersticks’ score raining down Cupid’s arrows all around. 

Jean, a stoic who proves to have his limits, at this stage just leaves them to it. The short shrift Denis gives to Colin’s character from then on, save for one hotel-room tumble, is rather a shrugging treatment of this supposed amour fou, as if Denis doesn’t think it deserves to be considered anything more than a reckless folly. The sex scenes have nothing on the thrashing repercussions.

Binoche has not played a character this deceitful, overwhelmed, or childishly self-serving in ages: filmmakers who worry more than Denis about audience sympathy might have eased off here and there. Her fury of being accused of what she’s literally doing is worthy of one of Bette Davis’s Jezebels, tipping the film into high melodrama while it clings on to a certain acrid credibility.

Lindon, ever-indispensable, is terrific, thriving even more in the side plot about his feckless teenage son (Issa Perica), a biracial school drop-out who’s been living with grandma (Bulle Ogier) and rinsing her credit card. He gets called out by Jean in one punchy diatribe about using identity politics to shirk individual responsibility: a stinging rebuke to prevailing discourse, even if it could easily belong in another film altogether. 

Watching these characters mask up, sometimes with a strange inconsistency that’s rather authentic, as they go about their business, it’s clear this film will feel like a time capsule. Sara and Jean’s relationship has presumably been a victim of classic lockdown strain, even if Denis doesn’t choose to press that point. She’s mainly giving her actors a workout, as if encouraging them to clock up some histrionic gym time so those muscles don’t go to flab. The film has an impetuous, let’s-try-it-on quality that makes it a modest pleasure.

Cert TBC, 116 min. UK release date TBC