Ballett Frankfurt, Sadler's Wells, London<br></br>Rennie Harris, Peacock, London

Now you don't see it, now you still don't see it. Except you do

Here's a proposition. Take two unconnected monologues about love affairs and place them side by side on a stage. Take two dozen conference tables, and stack them on their sides to create rooms. Take a bunch of dancers, and have them embody the emotion of the two stories, but hide them behind walls. Take video cameras and screens, and offer the audience (who thought they'd come to see something live) what is in essence a live-recorded film.

William Forsythe's latest, extraordinary work (and his last, for Ballett Frankfurt, now that the city has pulled the financial rug from under him) bears the title Kammer/ Kammer. This refers, I think, not only to the bedrooms where many of the intimate events recounted happen, but more importantly to the kind of exploded double-chamber work Forsythe has invented. For Kammer/ Kammer is unlike anything seen before in theatre or cinema, still less from a ballet company. And it is the unlikeliest success. It is vast and dislocated in physical terms, yet achieves a pressing intimacy as spoken details accumulate. By restricting the audience's gaze (we might catch glimpses of wrestling bodies through gaps, from time to time, or a flying ankle flicker above a wall), Forsythe condenses its emotional charge. And this feeds, drip by intravenous drip, into the increasing tragic tension of the two confessional stories about love.

Forsythe is blessed in his two protagonists, who give Oscar-worthy virtuoso performances, so believable you fear for their sanity, and also bitterly funny. Antony Rizzi is a young Woody Allen in a sock hat, bemoaning the inequalities of his relationship with his male rock star lover (using text adapted from the novel Outline of My Lover by Douglas A Martin). His predicament is the more familiar, and we feel superior enough to laugh at his clumsy attempts to describe the scale and complexity of his feelings.

Dana Caspersen's Catherine Deneuve, or rather, an actress kidding herself she is the French film star, is trickier to decipher, as she recalls her passion for a girl student in her university seminar group where she is a classics lecturer. Even though she doesn't actually dance, Caspersen's performance is a fine physical study, as she strides about peremptorily in little Chanel suits that expect to be obeyed, smoothes her immaculate sweaters and settles her face in a brittle mask of composure. All this makes her failed amorous fantasy all the sadder.

I set out wanting to hate Kammer/ Kammer for its maddening complexity, its pretentious theorising, and its sheer crazy scale. But Forsythe's puppet-master control is so aware of every resonance, including the effects of humour and bring-the-walls-down chaos, that I find myself in awe. This is a man who has never been content to take art forms as he finds them. Here, he has created a hybrid in an attempt to say something that none of those disciplines could say by itself. What we learn about love, by the end, seeps out through the gaps.

Philadelphia-born Lorenzo "Rennie" Harris is a more obvious kind of message bearer. Through his shows based on the hip-hop moves he learnt in the Philly badlands as a boy, he hopes to promote cross-cultural understanding. It's not that he condones gun culture and gangs. But, as he explains in the programme booklet of his new show Puremovement - a resume of the past 10 years' work for his company - he has "personal history and issues" that need airing. For Harris, "recognising lineage" is one way to a better world.

The most obvious expression of this is in Rodney Mason's rap monologues, great lava flows of alliteration, anti-war tirades and wordplay. The five dance pieces, mostly from the early 1990s, are at their best, though, when celebrating simple physicality. There's something bracingly straightforward about the way Puremovement's seven hunks display their personal charms and floor skills. Feet float on invisible conveyors, electric currents jigger through creamily muscled bodies. There are handless headspins, one-armed handspins, and legs flying out like flags in a breeze.

Not everything takes flight so easily. A sequence of potentially hard-hitting stills projections of Philadelphia slum landscapes is the wrong shape for the stage aperture, and just doesn't work. But the funky music is first-rate, and the authentic feel overall leaves last year's Bounce looking lame.

jenny.gilbert@independent.co.uk

Rennie Harris: Birmingham Hippodrome (0121 622 7486), Mon & Tue; Lyric, Belfast (02890 272626), Thur & Sat; Sheffield Lyceum (0114 249 6000), 3 & 4 Nov; Manchester Contact (0161 274 0600) 6-8 Nov; Brighton Dome (01273 709709), 11 & 12 Nov; New Wolsey, Ipswich (01473 295900), 13-15 Nov