Improbable have never before been part of bite at the Barbican, so their new show about the Great God Pan – and the little god Pan, too, with his cheeky smile, gimlet eye and hairy haunches – is a landmark of sorts.

All sorts, in fact, as Panic – directed and designed by Julian Crouch and Lee Simpson – is a mixture of confessional anecdotage, historical summary, cut-out home-made imagery and phallocentric fellowship.

Phelim McDermott is clearly Pan, bright-eyed, curly-headed and paunchy, and he’s soon Pan in pants, stripping down to his underwear. His three nymphs are Angela Clerkin, long-time Improbable member, Phelim’s former PA Lucy Foster, and aerial artist – she twists down as a nocturnal vision at one point – Matilda Leyser.

I’d never thought of Pan having prostate problems before, but McDermott is soon telling us about them, and transporting us from the forest to his apartment in Brixton which is crammed with self-help books, one of them with an introduction by Maureen Lipman (why that’s funny I don’t know, but it is), and then translating himself back into Pan-ship by doing his gyratory pelvic exercises and cloven-footed funny walk.

For as Panic is rather like one of those Ken Campbell one-man shows “with other people”, investigating aspects of Pan under a series of headings and forcing the discoveries into an overall ragbag monologue. Some of this comes into the “too much information” category, as in the episode about picking scabs. Pan was an Arcadian deity as well as the god of rape, however, and McDermott ingeniously conveys both aspects of the character.

The nymphs have their moments, too, with mini-monologues amid the posing in paper trees and appearing with paper bags on their heads. McDermott’s funniest sequence finds him afflicted with a huge haystack of a penis, trying to park it somewhere while disclaiming, “You don’t get that down the IMAX; talk about 3-D...”

There’s a forest orgy conjured by mini-puppets in silhouette, an explanation of fear and panic all down to the deity, a falling-over scene in which Pan is assailed by labyrinthitis and an idea of Pan as a therapeutic lover, this time recounted by Leyser, who tells us that she feels it her duty to sleep with as many boys and girls as possible. Finally, McDermott toasts the nymphs in their own tears, a lovely touch with a piercing, retrospective resonance.

- Michael Coveney