The Alchemist, Courtyard, King's Cross, London

Wherever there is greed, there is gullibility, as any con man will happily attest. But it may not just be crude covetousness that drives the willing victims of such deceptions. It may be a token of their desperate need to believe in something.

That's the shrewd perception Ben Jonson hilariously elaborates in The Alchemist through the chaotic misfortunes of the gaggle of dupes lured to a London house where the duplicitous caretaker servant Jeremy, now known as Face, has installed fellow tricksters Subtle, a bogus alchemist, and Doll Common, a whore.

This trio may not know how to turn base metal into gold, but they are adept at other types of transformation. This manifests itself not only in the quick-change artistry that enables them to scramble into almost as many identities as they have clients. It's also evident in the weirdly alchemical effect of their trickery on the saps who seek their services. With a little artful nudging, ambitions that were dull and limited take absurd flight, and the house becomes a wonderfully wonky dream-factory. It's not therapy being offered here; it's just that the gulled are taken out of themselves, before being left beside themselves. Gulls just wanna have fun.

Lucy Linger's stagingis competent and gets decent laughs, but it doesn't get much below the surface of this drama's manic hilarity and metaphoric richness. The action has been relocated to a vaguely realised present. Apart from Face, Subtle and Doll, the roles are doubled. Doubtless this is because of budgetary constraints, but it blurs the division between the tricksters and their protean skills, and their hoodwinked victims.

With the audience on three sides of the acting area, the staging ideas create as many problems as they solve. Doors are represented by thin rails, so that the characters seem to be arriving and exiting through security barriers. This means that we can see the gulls as they nervously prepare to brave the dream factory (slicking down their hair in the hall mirror, etc) and the con artists as they listen for their entrance cues (for example, we see Rebecca Reaney's blonde, tarty Doll stick her chewing gum on the wall before sashaying on in her guise as the intermittently raving daughter of a great lord. This robs the farce plot of velocity and comic tension.

Edward Dehn as Subtle and David Beckford as Face are good at suggesting the tensions in the relationship of this devious double-act that result in the shocking betrayals of the last act. Nippily shifting between impersonations, Beckford has the right bare-faced outrageousness, but when he has to revert to being Jeremy, the servant, at the end, there isn't a sufficiently eerie sense that this is just a default position rather than a true identity.

To 25 January (020-7833 0876)