The Brandstrup-Rojo Project, Linbury Studio Theatre, London

Bach's 'Goldberg Variations' have inspired a mini-masterpiece

Audiences don't often get the chance to see the preparation that goes into a performance. And why would they want to, you may ask.

Well, for one thing, it humanises the dancers; for another, it illuminates the dance, and it's a fascinating process in itself. This last provides the motivation for Kim Brandstrup's latest project, which brings together a handful of dancers from the Royal Ballet, an equal number from contemporary and street dance, a pianist, a grand piano, and Bach's formidable Goldberg Variations, and throws them all into a rehearsal studio.

What could easily have been an eclectic jumble emerges as an ingeniously organised, frequently humorous, gently enigmatic and wholly luminous hour and a quarter – a mini-masterpiece, in short. The only frustration is that the week's run at Covent Garden's Linbury Studio sold out before it even started, and the chances of a repeat season look remote, given the diary of its star Tamara Rojo, whose serene command of her art superbly balances the rigour and intricacy of Bach.

Goldberg begins, as all dance rehearsals begin, with someone opening a door, entering a room and letting in light. It ends, as all rehearsals end, with a final darkening and closing. In between, groups of dancers straggle in and out, do their warm-up stretches, watch their colleagues, practise steps or fall asleep. A bulky old TV set, its back to the audience, intermittently holds the group's attention. What it's showing, you slowly realise, isn't an episode of Family Guy but choreography, and Brandstrup homes in on the curious hand jive that dancers use as a shortcut to learning steps and turns it into a performance.

The most obvious difficulty in using the Goldberg Variations is their length and format, there being 30 of them, ranging from earthy to sublime. Brandstrup divides them into groups of five, using the closing of the studio door and switching-off of lights as a natural divider (the superb lighting design is by Paule Constable). Mostly the music is live, played by Philip Gammon in the foreground. Short sections sometimes emerge tinnily from the TV set. One bit gets piped through a dancer's iPod. Importantly, though, the work is delivered complete, and the temperature of the activity in the studio carefully calibrated to rise to the glorious No 25, the so-called "Black Pearl", the longest of the variations and the work's emotional heart.

Human stories emerge discreetly as the music dances on. Rojo, immaculate in a black silk frock, sits apart from the others, a little aloof despite touching attempts to be playful. Tom Whitehead, a Royal Ballet colleague, cuts a swaggering figure as he stalks into each session and shrugs off his jacket, using Rojo as a coat stand. She clearly longs for the intimacy of their duets to colour their off-duty relationship, but is disappointed (a minor objection here: who, in their right mind, rejects Tamara Rojo?). Downstage, so motionless that for ages you assume he's just the page-turner, sits ballet principal Steven McRae, whose leaf-in-the-wind agility Brandstrup exploits in a series of puckish solos. Is he Rojo's secret admirer? Tantalisingly, we're never sure. Even when they finally dance together there is a distance, a reluctance, in McRae.

The same subtlety extends to the treatment of the non-classical dancers, all very fine. Another choreographer would have seized on Tommy Fran-zen's hiphop virtuosity as a chance for dazzling display. But Brandstrup is more interested in finding common ground, and seeks out the softer, flowing qualities of street dance. Similarly, he's fascinated by the subtle emotional shifts that occur when dancers move from practice mode into performance. Finding the means to amplify those details to such riveting effect is a major achievement.