Sankai Juku: Kagemi, Sadler's Wells Theatre, London

They may be ultra-slow, impenetrable and downright weird, but Sankai Juku performances gather enthralled audiences. What do they think they have been watching? A series of perfectly composed moving tableaux? A freak show, on the edge between serious risk-taking and grotesque sensationalism? Or philosophical profundities, perhaps?

Sankai Juku's latest show to hit London, Kagemi, created in 2000, is all those things. The philosophical profundities, though, I take on trust. This is the Japanese dance or physical theatre form called Butoh, after all. It's not that evocative elements are totally absent, but precisely what they add up to is anybody's guess.

Divided into seven tableaux and performed by seven men (seven is a favoured Sankai Juku number), Kagemi apparently translates as "Beyond the metaphor of the mirrors". What that means visually is a spare but theatrically stunning stage. A disc at one corner operates mostly as a podium for solos performed by the company's founder, choreographer, designer and leading dancer, Ushio Amagatsu. A large square expanse of outsized flowers rises to become a suspended canopy and reveal figures buried underneath. Thematically, the notion of mirrors emerges frequently.

But what exists beyond the mirror? Sometimes the performers might be babies, rolling to the floor and squatting, mouths gaping in noiseless howls. And maybe Amagatsu's long travel down a lighted runway represents life's journey.

Amagatsu's solos are so slow he is in danger of becoming a Japanese Lindsay Kemp. He might be floating. His arms undulate weightlessly and his silhouette seems fringed with a vibrating light, so that you think you are hallucinating. The six other performers, also shaven-headed and covered in white chalk, recall the ivory figurines of oriental art - a fisherman, a vendor, a carpenter - except that here the tools are missing and they are sexually ambiguous. Their dance is supremely stylised, their faces are masks of fixed expression - tragic, laughing, neutral - as in traditional theatre.

The stylisation produces a distancing effect, accentuated by the frighteningly extra-terrestrial appearance of everything. You are alienated, disoriented. The collision of Sankai Juku's strange slow motion images with slabs of orchestral music and pounding sound is theatre at its most outrageous. The theatricality lasts to the end with the other-worldly deliberation of the curtain calls - performers clutch crimson flowers to their white skin and bow - becoming a whole art form in itself.