I Don't Believe in Outer Space, The Forsythe Company, Sadler's Wells

An audience favourite has a USP that fills the house as long as they maintain the suspense - with William Forsythe, it’s the quality Diaghilev prized: unpredictability. When he set out in Germany in the 1980s he evolved an extreme classical ballet. Just as people got used to his distortions, he went into conceptual theatre. Expected to be gnomic and abstract, he then did emotional dance-theatre about his young wife’s death. Now to comedy territory in I Don’t Believe in Outer Space, which is only on for two nights at Sadler's Wells, indicating that his old London muckers worry about this unpredictable man. Last night’s ovation indicates they shouldn't worry.

Though about two-thirds of this 80-minute show is padding, what works is cherishably funny and accessible, lunar lunacy. The setting, for one thing, is a stageful of what look like giant rabbit’s droppings or perhaps meteorites, in which the crowd skitter about like Clangers in an earth tremor. Also a great torrent of text is vomited out almost incessantly from one or other of them, sometimes being highbrow and cod-intellectual, sometimes stringing out, line by line, with mischievous timing, the lyrics of “I Will Survive”.

Suiting the title, the whole thing has a claustrophobic, defiant atmosphere, a deliberate randomness of strips and bits all balled together. The lighting mixes many variations on half-dark, and the Thom Willems score alternates soft outer-space throbbings with half-music woven apparently from threads torn from different jazz songs - this bass line, that keyboard part, some other melody - the effect being discombobulating, and throwing the ball of litter firmly to the audience to unpick for themselves.

But fortunately there is a bona fide star glittering in the middle of the anonymous crowd of teetering, randomised people in vests and jeans. Forsythe’s second wife, Dana Caspersen, is a quite extraordinary performer, something between Jim Carrey in The Mask and Robin Williams's genie in Aladdin.  Built like an acrobat, with wispy hips and bird legs, she shifts shape and character effortlessly with both voice and body, as if being Photoshopped before your eyes.

She gives a hilarious opening dialogue apparently imagined between a witch-like crone of monstrous intentions and her neighbour, a prissy, girly-voiced wife who has made the mistake of inviting her to a meet-the-neighbours’ party. As Caspersen voices the cackling monster woman - “Hello!!!” never sounded more like hell from the first syllable - her body collapses in on itself, all jags and angles and bony, grasping fingers, a gargoyle almost crushing herself from inside. In a trice, as she voices the other woman, the body snaps up into a tiny, scared, pigeon-toed doll, nose high and frightened, voice squeaking with desperate courtesy about tea and houses and an even more desperate fear. Crone-girly-crone-girly, Caspersen is dazzling, a one-woman stand-up panto, every flinch and lunge cut with a superb precision from close observation by a master-jeweller of moves.

At most other times I found it as mystifying as watching monkeys in a zoo. The 18 performers twitch and itch, scream earsplittingly, caper with the droppings, show no sense of intention whatever in their scuddings about. It’s as if they were all mad in the same way, had all lost their bearings and common understanding. But then sometimes it livens into a lunatic dance of a sort - a man jives with artificial buttocks thrust amusingly down the back of his jeans, the bums bobbling as they lose their anchorage. Even funnier is a potty ping-pong bout with a hyperactive hoodie with two bats dancing about in hugely unfair advantage over his opponent who has no bat at all.

There’s an episode of mayhem that grew on me, where Caspersen runs about declaiming hypnotically, “As if by chance, all kinds of stuff is moving, everything is all over the place... as if by chance, things fall”. This comes across as simultaneously the ravings of a dope-smoker unable to hold a thought down, and also gradually a reference to the nature of accident in relation to mortality. The formula darkens at the end, when Caspersen changes it to: “No more... no more stopping, no more going, no more running with your brother down the track in wintertime. No more parties, no more husbands.” It is impossible not to think of the death at 32 of Forsythe's first wife in 1994, and his second is a sensitive angel of death.

This production’s entertainment factor is partly in how quickly the audience laughs as it recognises a song is creeping into the text. One particular high has a baroque operatic-style recitative by tenor haranguing Caspersen in crone mode, and as she lies broken-legged and petrified on the ground, she gargles horribly, “You think I’d crumble, you think I'd die” And shrieking, she’s dragged off: “I will survi...!” It’s almost Sondheim. For such deliciousness, I can forgive the two-thirds padding, but truth is, this is Dana's show.

• The Forsythe Company performs I Don't Believe in Outer Space at Sadler's Wells tonight, also 5-7 May, Desingel, Antwerp;  Forsythe’s The Defenders is at Rockenheimer Depot, Frankfurt, 30 Mar-10 Apr; a Forsythe world premiere 9-12, 16-25 June, Hellerau, Dresden
• Tonight at 6.15pm Forsythe is in conversation with critic Roslyn Sulcas at Sadler's Wells. Phone 0844 412 4300.
  
• Q&A Special: William Forsythe Over Time on theartsdesk
• The Forsythe Company website
• Find William Forsythe's From a Classical Position DVD on Amazon
  

Watch Sylvie Guillem lead the Paris Opera Ballet in Forsythe's In the middle somewhat elevated in the late 1980s