Alan in Belfast: Both Sides of the Blade – Binoche plays an ageing lovesick teenager trapped in a troubled melodrama (QFT until 15 September)

Both Sides of the Blade is a film about living well with the choices that you and other people make, thinking carefully before revisiting them if unexpected opportunities arise. A pretty mundane, everyday premise you might think. But director and co-writer Clare Denis has crafted a wobbly love triangle to torment audiences over nearly two hours.

When you stand up in shallow water, the calm surface can disguise dangerous undercurrents that could sweep you off your feet, losing your balance and being sucked away from safety. Both Sides of the Blade begins with Sara (Juliette Binoche) floating in an idyllic bay, smooching in the strong arms of her rugged husband. But what danger lurks beneath them?

She’s a serious afternoon radio presenter who unpacks international affairs and the issues of the day with expert talking heads, while Jean (Vincent Lindon) is a divorced ex-rugby player and ex-con (probably for some kind of financial misdemeanour given his lack of easy credit) who finds it tough getting work.

Gradually the clear water is muddied by the return of Francois (Grégoire Colin), a man familiar to them both, and to whom Jean is second best in Sara’s past. Distressed strings play over Francois and Sara’s first meeting in a decade or more. Soon she’s talking to herself in the mirror in case cinemagoers can’t already imagine the “love, fear, sleepless nights and the phone at my bedside” that are to come.

Poor Jean can foretell how other people’s lives could unravel and leave them unfulfilled, but he can’t seem to put this talent and energy into stopping his own world flushing itself around the U-bend and into the stinking Paris sewers.

The film descends into scenes or Binoche in bed, in the bath, and frequently in the buff … and not in the sense that the prized French actor is showing naked emotion. Her whole character’s USP is that she will argue that black is white, that what you saw is not what happened, introducing specious distractions, assigning motivations to other people’s actions, shifting blame to cover up her desires, moaning “mon amour” to her current husband while scheming how to pour lighter fluid on the glowing embers of unrequited love.

A string of ultimatums suggest that all three protagonists have much to lose. A side plot with Jean’s son Marcus (Issa Perica) seems merely an excuse for the dad to spend time away from Paris. Jean’s dialogue frustrates: overly halting when speaking to both his wife and mother. The Paris apartment’s balcony simmers like Chekhov's gun, completing the betrayal of Claire Denis’ film.

The finale – technically unlikely in real life – is a fitting finish. Watery scenes neatly booked the movie. The performances from Binoche and Lindon are very strong throughout. But that can do little to redeem this unsatisfactory screenplay and its wobbly exposition.