Zahid Mubarek should have turned 25 this month. But in 2000 he was viciously attacked by his cellmate as he lay sleeping on the eve of his release from Feltham Young Offenders Institute. He died seven days later.

It took a scandalous four and a half years for the Government, under pressure from the Mubarek family, to agree to a public inquiry into his murder. The report is due next year. In Gladiator Games, Tanika Gupta combines verbatim text with dramatisation to portray a chain of events so horrifying, so shameful and so avoidable that it beggars belief.

When he arrived at Feltham, Robert Stewart had already been involved in the murder of a fellow prisoner at HMP Hindley; he was also a known racist and acutely mentally unstable. Yet he was locked up with a young Asian serving time for the theft of £6 worth of razors and interfering with a motor vehicle.

Every aspect of the situation is questionable: why was Mubarek imprisoned for such a minor misdemeanour? Why did no one at Feltham take account of the risk Stewart posed? One appalling explanation offered to the inquiry was that the pair may have been exploited in a prison officers’ game known as Gladiator, whereby inmates thought likely to clash violently were deliberately confined together and bets placed on the outcome.

What the production powerfully suggests is that Zahid’s death occurred in an environment rotten with institutionalised racism.

Gupta’s writing and Charlotte Westenra’s production for Sheffield Theatres and Theatre Royal Stratford East have a televisual quality. The non-verbatim dialogue is sometimes soapy, and Niraj Chag’s foreboding score can be intrusive.

Otherwise, the approach works extremely well. Paul Wills’s design suggests the grim, echoing austerity of Feltham and supplies a suitably adversarial setting for the inquiry, speeches from which are delivered from steel walkways surrounding a tiled square that represents Mubarek and Stewart’s cell. This creates a gripping split-screen effect, offering a simultaneous double perspective on the unravelling tragedy and its aftermath.

It is agonising to watch Ray Panthaki’s Zahid tolerating his cellmate’s threatening behaviour and quietly longing for an end to his sentence that we know he won’t live to see. And Tom McKay is genuinely frightening as the deeply disturbed Stewart, a tattoo reading RIP etched across the brow of his shaven head above a face contorted by hate and childlike fear.

This is work of real political importance; painful to witness, but entirely essential.

Box office: 0114-249 6000 until Oct 29, then at Theatre Royal Stratford East 0800 1831188