The Dead School, Tricycle Theatre, London

In the wildly funny and piercingly poignant The Dead School, an expressionistically dilapidated classroom in a Catholic school in Ireland – or rather a morbid, ramshackle version of it that's been reconstructed in the home of a mad former master – becomes the site for a freewheeling phantasmagoria in which the intertwined fates of two schoolteachers of different generations are resurrected and subjected to a blackly exuberant autopsy.

Adapted from the 1995 novel by Pat McCabe and directed with a fierce flair by Padraic McIntyre for Nomad Theatre Company, the stage adaptation is like a wacky amalgam of the Nighttown episode in Ulysses, Under Milk Wood and Strindberg's The Ghost Sonata. A blackboard on which the word "POETRY" has been scrawled can split apart like double-doors to reveal the padded cell in the London asylum to which the younger teacher is bound. Living statues of eminent statesmen – Daniel O'Connell, Gladstone – can chip into the petty squabbles that keep breaking out between protagonists and the moveable-feast chorus of small-minded gossips.

The combination of the distorting rigours imposed by religion and the strains of being a teacher in a Catholic school is enough, we increasingly gather, to drive men mad. Sean Campion is in devastatingly good form as Raphael Bell, who started off a driven, idealistic teacher who took the school choir to two historic appearances on Radio Eireann. Childlessness, ossification, the traumatic discovery that his star pupil has declined into skag-addicted adulthood: these and other blows see him dwindling into an alienated bigot.

Like a junior counterpart further down the evolutionary spiral, Nick Lee's superb Malachy Dudgeon starts to come unravelled after the accidental drowning of a pupil and his wife's desertion of him for a rock-band singer.

The piece is full of deliciously fast, take-it-or-leave-it comedy (Malachy's arrival in the big city done as a parody of Jon Voight arriving in New York in Midnight Cowboy) and the gut-wrenchingly grievous (Raphael's achingly low-key departure for suicide in the local lake). Yes, the story-telling could sometimes be clearer; yes, it feels slightly too long. But it's wonderful – at once an indictment of Irish Catholicism and, theatrically speaking, God's plenty.

To 13 March (020 7328 1000)