Mother Courage and her Children, Olivier Theatre, London

Smitten by this hyena of war

Often I sit back and watch you, amazed," the smitten Chaplain tells Mother Courage in Tony Kushner's bouncy new translation of Brecht's greatest play. He could be speaking for the entire audience in the Olivier, where Fiona Shaw is delivering a phenomenal performance as this war-profiteering "hyena of the battlefield". The actress's dynamism is matched by the extraordinary vitality of Deborah Warner's modern-dress production which keeps faith with Brecht's staging theories, while smashing through the po-faced pieties that normally attend them. Giving a wacky twist to the trappings of epic theatre, it feels about as hidebound by convention as a piece of urgent, breaking news.

While the audience take their seats, the stripped-back stage swarms with technicians and stage-hands who return to expose the show's inner workings in the dislocating bathos of the between-scenes black-outs. There are ear-splitting explosions and the place-name sheets of Tom Pye's excellent design are experimentally winched up and down. Nothing prepares you, though, for the outrageously triumphalist arrival of Shaw's heroine, enthroned in a garden chair atop her mobile canteen and accoutred in dark glasses and piratically puffed-out skirt. It's like a parody of a rock star's entrance to a stadium – an impression reinforced when she grabs a microphone and frugs her way through the raucous introductory song.

Dragging her cart in the wake of the army, Mother Courage loses all three children through her deluded belief that she can keep them safe by playing the small business-woman. She fails to understand that she's merely a pawn in war's much bigger economic game. By English actresses, she's often portrayed as a dour Northern battle-axe. In a performance that ranges from buccaneering bravura to washed-out, stoic endurance, the Irish Shaw refreshingly emphasises the swaggering resilience as well as the flinty resourcefulness. There's just the right challenging clatter here of Brechtian contradictions, as Courage struggles between her maternal and entrepreneurial instincts. In the matchless sequence, for example, where she has to pretend ignorance of her slaughtered son, Shaw wrenches her features into a tight facial shrug that trembles on the verge of turning into a tear-stained mask of tragedy. And she brings a wonderful, aggressively disguised sensitivity to the scenes with her mute daughter (Sophie Stone) in which she's forced to dodge the hailstones of her own remorse.

This is, throughout, a creatively controversial production. Instead of offering the usual harsh harangue, Duke Special's music has a quirky melodic plangency, but the mysteriously pacific presence of this gentle, dreadlocked composer-singer is itself a kind of alienation effect, given the strife-torn circumstances into which he strays. There's witty work from Stephen Kennedy and Martin Marquez as, respectively, the Chaplain and Cook, and Colin Stinton turns in a caustic cameo as a crazed, gung-ho American general.

To 8 December (020-7452 3000)