Happy, The Pit, Barbican

Until last night I thought marionettes meant either the widdly-waddly walk of Thunderbirds or the breathless kitschery of The Lonely Goatherd.

Until last night I thought marionettes meant either the widdly-waddly walk of Thunderbirds or the breathless kitschery of The Lonely Goatherd. I thought it was an artform that had been handed its P45 by animation. But Ronnie Burkett, a Canadian puppeteer, has breathed new life into it ­ new and sublime life. The same strings, the same centuries-old limitations but suddenly the world is transformed, flooded with light.

No box set ­ instead a four-sided, rotating Welsh dresser; white strings instead of black; a man in an apron and jeans standing among his puppets, quite visible, part of the action and yet utterly forgettable. He does all the voices, all the string-pulling, aided only by a stage manager to hand him either puppet or prop.

No, hang on, these aren't puppets, they're real people (apart from the dog and cat): the faces are so expressive, so evocatively carved that you find it hard to believe they're not moving.

And were you expecting a simple story that unrolls from beginning to end? Through a mixture of monologue and dialogue and surreal chorus, a weird and unforgiving story gradually pieces itself together. Drew and Carla are young and in love, but in an instant he's dead from an aneurysm. Carla seeks solace in her poetry but also from the other residents of the rooming house. Lou, a superannuated vamp, has little to offer beyond a strategy for keeping men quiet. Raymond, the caretaker, is too lonely to help. And Happy, well, he's too happy.

Yet each character's story transforms into something quite the other. This is a play about grief and happiness: how do some people shrug their misery aside and why do those like Carla find the future impossible? And where does memory fit in ­ is it essential to remember in grey, if only to preserve the colourfulness of real life?

And, more to the point, how do knee-high string puppets somehow make all this zing with a realism I have rarely experienced, even with the cream of Equity? Is it something to do with their purity?

I still don't know, but too many moments stick out: Frank, beret on head, forcing a concentration camp skeleton back to life; Happy, swinging on his park swing in the rain; Lou's knee-slumpy coughing fits; and the basset hound's bum biting. Or Carla sitting forlorn on a chair in her dead husband's pyjamas and sweater.

Yes, these are puppets I'm talking about. Who cares? Happy is a monumental achievement ­ two unstinting, unbroken hours of word, song, minuscule gesture, inventiveness, surrealism and humanity. And if theatre's about transcendence, about wonderment, this is the best theatre in London.