Shivered, Southwark Playhouse, London

When some artists affect to say the unsayable, the result is simply unspeakable. To listen to some folk, you might run away with the idea that Philip Ridley - renaissance man of the East End and master of the sawn-off baroque - is just a sensationalising miserabilist out to exploit and maximise everything that is morally and viscerally gross and triple-X rated.

But those who judge him to be that seem, to me, to be responding to a prose paraphrase of his work and one of their own making. It is not Ridley who is desensitised; it is his attackers in their fixed and laminated indignation. They fail to take on board the generosity of spirit that impels his plays and makes them not a tragicomic revelling in the destructive element but bravura, abundant, tonally varied tours de force of the dramatic and narrative arts. His invigorated manner and visionary verve incorporate - without resort to moralising speeches - the resilient, healthy values that are like a built-in antidote to the sick situations he (often clairvoyantly) depicts.

As in Tender Napalm, his excellent last piece, Shivered tells its story in emotionally eloquent temporal shifts. It is set, over a decade, in the fictional Essex new town of Draylingstowe, built round a car plant run by the Japanese. During this period, the plant closes and the town declines, leaving in its wake physical deformity and disturbance in the family of a trade-unionist car worker and his wife Lyn (excellent Olivia Poulet) who, after a terrible bereavement, turns to a kinky-sex-and-torture vengeance. Unable to find employment, the older son, Alec, joins the army and is beheaded by jihadists who post a video of it on the internet.

In Russell Bolam's beautifully acted and designed production, one of the central focuses of interest is the relationship between the clever, UFO-obsessed younger son Ryan (superb Joseph Drake) and his rather dim mixed-race sidekick and tormentor Jack (Joshua Williams) who - with the precocious cynicism of those weaned on the Pandora's box of the internet - is fixatedly suspicious that the beheading might have been faked. Eventually, he forces the boy to authenticate it by watching the atrocity and even then is not convinced.

This is key to a play that teems with fakes and techo-induced callousness, including an obese charlatan healer and (as we discover in a tense, brilliantly cast flashback to a scene between soldier Alec and his father) bogus heterosexuals. Some find it extraordinary that Ridley is also a master of writing for children. But again that is to fail to feel the potential for magic that the adult plays, where innocence (as here) is so violated, long to get back to.

To 14 April; 020 7407 0234