Edward Gant's Amazing Feats of Loneliness, Soho Theatre, London

It's a clever way of dressing up horrors to reinvent theatricality. So, a facially deformed Italian lady can squeeze her pimples to produce pearls, or a trepanning operation performed by a phoney old fakir in Nepal results in a lovelorn bereaved gent plugging the hole in his head with a filthy cork. The fakir himself, Ranjeev the Uncomplicated, is a music-hall blackface who admires the English for being at their most stylish when style is least required. It must always be remembered that Neilson is Scottish.

These are details in the two main stories offered by the fictional impresario Edward Gant – prodigy, soldier (he survived the Charge of the Light Brigade), traveller, poet – on the night of his very last presentation. Gant, vulpine and sinister in Simon Kunz's creepily conducive performance, appears on Tom Scutt's atmospheric fit-up design of bare boards, plush curtains, footlights and gilded pilasters, with ingenious scenic amendments.

Gant's small but perfectly formed company comprises a stone-faced, fellow military veteran Jack Dearlove (Sam Cox), the twittering, egg-laying Madame Poulet (Emma Handy) and the richly vocalising but increasingly cynical Nicholas Ludd (Paul Barnhill). All three play with a delightful flourish and precision, sideways on to the music hall "reality" of the show.

The deformities on show, says Gant, with a smug leer, are not the deformities of the frame, but those of the heart and mind. These amazing feats of loneliness he has culled from scouring every continent, though of course the largest distortions are those emanating from his own twisted imagination.

The device of a travelling freak-show is not just a sweetener, though, but is fully enjoyed for its own sake, as evident in the design, fully maintained in the lighting of Malcolm Rippeth, the atmospheric soundtrack of composer Tom Mills and the succession of theatrical tricks involving disembodied heads, swishing scenic curtains, flickering footlights and copious squirtings and spurtings of various liquids and bodily fluids.

At one point, Ludd intervenes as a rival suitor to the pock-faced Sanzonetta, and squeezes a huge carbuncle that yields only pus and cheese. But this emission is topped at the end as the strange performance collapses amid disharmony in the ranks when Poulet and Dearlove throw off their bearskins (don't ask) and Ludd questions the validity of Gant's show-business credentials and, indeed, show business itself.

Ludd bemoans the fact that, thanks to the irresponsible foolery of Gant, he is now the loneliest creature on earth and doomed to an eternity of self-loathing. His situation is aggravated by the bear asking for a few pennies for an imaginary cup of tea and a full-scale teddy-bear's picnic ensuing.

This is all fairly funny, though a bit over-extended, as Gant has half exposed himself as the Phantom of the Dry, fuelled by opium and the line-forgetting misfortunes of colleagues. You feel that Neilson is further justifying his reputation for malevolent whimsy when Madame Poulet disconsolately enquires if she can now be excused to remove the backstreet abortion from around her neck.

Suddenly the show reveals an alarming desire to veer dangerously in another direction, but it's still hard to resist a piece where the tone is, for the most part, so deliciously maintained, and in which an ardent lover deserts his mistress for an expressive oyster who has mystery; Gant is seen discussing the next move with his chum, stretched out on a small table standing at 90 degrees to the floor; and a chinless wonder places his faith in curing spiritual pain through meditation, song and deep massage.

To 11 April (0870 429 6883; www.sohotheatre.com)