Foxfinder, Finborough Theatre, London (4/5)

There hasn't been a bumper yield of great new plays this year, but now, at the eleventh hour, comes this spell-binding dystopian parable by Dawn King.

The winner of the 2011 Papatango New Writing competition, the piece is realised with an absolute imaginative authority in Blanche McIntyre's tense, darkly atmospheric production which is performed on a narrow thrust stage of bare boards at the Finborough.

We are in an alternative or near-future England where the “red beast” has become public enemy number one, held responsible for everything from the worsening weather and the failure of the crops to the manipulation of people's dreams. Samuel and Judith have had a dreadful year. He was unable to work after the accidental death by drowning of their toddler son. Inability to meet the production quota, in a world of rations and scarcity, has brought their farm under suspicion of vulpine contamination. Hence the visit from young William Bloor, one of the “foxfinders” who have been intensively and monastically trained for the job from an early age.

Tom Byam Shaw gives an astonishing performance as this ascetic, fastidiously-spoken youth, arousing both terror and compassion with his eerie aura of brain-washed, other-worldly rigour and the fleeting hints you get of repressed distress, frustration and doubt. When alone, he indulges in bouts of self-flagellation and of chanting the credo of his masters. Kirsty Besterman is deeply sympathetic as Judith, a decent, intelligent woman who knows there are no foxes and can see through the twisted logic of a totalitarian regime which holds that the lack of any sightings is proof positive of the beast's especially pernicious slyness and that any show of disagreement amounts to collaboration with the foe.

This is not a new subject for drama (one thinks of the witch hunt in The Crucible) but it is developed here with an extraordinary purity of focus and a dreadful inexorability that does not preclude many surprising twists and turns before the predestined end. The irony is that the contaminator is William himself, his zeal infecting Gyuri Sarossy's troubled, glaring-eyed Samuel for whom imagined foxes and their mind-altering powers become a way of displacing his guilt about the death of his little boy. There's superb, creepy cross-lighting by Gary Bowman and an excellent, harsh and expertly unnerving sound design from George Dennis. All the elements of the production works with a rare creative coherence that will leave this play lodged in one's mind forever.