The inevitability of love turning angry and anxious is so ingrained an idea that we rarely question if it's so. Perhaps love and its opposite go together.

Perhaps it's what they mean when they say "for better, for worse".

It's not a theme often explored on stage, but I think it's what Akram Khan and Juliet Binoche are doing in their self-directed collaboration at the National.

The two are an unexpected pairing. London-born Khan is a star in the dance world, and although it's a small realm, his work needs no Tinsel Town glitter. Binoche, meanwhile, trails Hollywood fame which rather skews things, as fame always does. You can't help but wonder what this red carpet regular is doing in an experimental duet, albeit one with Khan.

The answer is "new experiences", as Binoche recently put it, and the result is in-i, a 70-minute duet that is not quite dance and not quite theatre. Through soliloquies and steps it depict a happy if misjudged romance that all too quickly shifts. In the opening scenes, you can almost hear the sensual static as the pair loop and curve, like two magnets, resisting each other then snapping tight.

Binoche is an unexpectedly able mover. Although not a trained dancer, she has a nimble, bendy bod, and remarkable stamina for a 40-something mother of two. She is also unstarry, with no make-up and a costume best described as bedsit chic. Khan also surprises, performing with all his stunning charisma but playing against type as a man poleaxed with sorrow. In one scene he bullies his own body into paroxysms of pain. In another he describes how he once loved a girl with blonde hair, only to be punished for wanting a "non-believer". "What if Adam was brown, and Eve white?" he cries.

In-i is not Khan's best work. Its dramatic arc is too speedy, taking us from happy to distraught in about two minutes. Another problem is that Khan is too angsty for too long, and there are some jarring theatrics for a minimal set (by Anish Kapoor).

There's also what I call the Curse Of Plenty. The National has so many resources it can't resist throwing everything at a production that needs only the charisma of its performers. With less largesse, and some emotional and theatrical remodelling, in-i would better convey the maddening misunderstandings of love.

Until 6 October. Information: 020 7452 3000, www.nationaltheatre.org.uk