Last Night's TV: Fallout, Channel 4

The word "fallout" is casual currency these days. It gets used to refer to the consequences of any action or situation, consequences that aren't necessarily serious, or even negative. Roy Williams may have been thinking of the word in that colloquial sense when he used Fallout as the title of his 2003 play about the aftermath of a stabbing, now brought to your television set as part of Channel 4's season on street crime. But if that was all the meaning he was interested in, he could just as well have called it "Aftermath" or "Consequences". I suspect that what he had in mind was the more precise original definition: the radioactive dust that descends after a nuclear explosion. A murder such as the one depicted here is a kind of Ground Zero; and afterwards the poison settles all around, contaminating the lives of everyone it touches.

To begin with, the action seemed deeply familiar, in a generic way: a boy murdered on an anonymous London council estate, for nothing more than his trainers and the kick of it. The boy, Kwame, was studious, polite, hardworking; the gang that killed him were almost a cartoon version of disaffected black youth: aggressive, contemptuous of authority (and, by extension, all adults), misogynistic, and filled with a seething, nihilistic rage at the world and one another. Everybody knew who committed the crime, but the police couldn't find enough evidence to make a case.

Pretty swiftly, though, as the focus sharpened, that fuzzy landscape came into prickly relief. The boy who committed the stabbing, Emile (Charles Mneme), was a thug; but you could see, too, that he might be something else, especially in his gentle, almost courtly relationship with the lovely Shanice (Gugu Mbatha-Raw). As the cracks began to show in the gang, and Emile feuded with the leader, Dwayne (Ami Ameen), it was partly because Dwayne was worried that Emile was a weak spot, partly because Emile represented a challenge to his authority, but also because Dwayne desperately wanted Shanice himself. In public, he made repellent cracks about her looking to get herself raped. In private, with her, he was a lovelorn little boy.

While Williams was concerned to engage the viewers' sympathies, it wasn't with any easy notion of explaining or excusing. Into the toxic atmosphere of the estate came Joe (Lennie James), a detective sergeant who was brought up there. He was supposed to bring "local knowledge" to the investigation, along with what his commanding officer queasily called his "obvious attributes". For a while, it looked as though this might be a straightforward issue play about police racism, as Joe's fellow officers sneered at the "poster boy" and made it clear by sarcasm and inaction (as they sat back and watched his car being stolen) that he was not One of Them. But as the investigation progresses, or rather didn't, the moral became more slippery. At first, Joe brought a streetwise edge to police work. In an early encounter with the gang, he called Emile "youngster", bringing the surly response "Are you my dad?" "I might be. What's your mother's name?" Joe said, grinning slyly with the satisfaction of a point scored. But his supposed connection became a source of frustration. He slapped one member of the gang, flirted with Shanice, prompted the testimony of the sole eyewitness, thereby invalidating it; and finally, boiling over, he beat Emile up. Between kicks, he gazed up at the tower blocks and told the boy, "It's fuckers like you that have dragged me back to where I started."

You could take this in several ways. Joe felt, as his white colleagues didn't, the awfulness of what was going on. At the same time, he was fulfilling their low expectations of how a black man might behave. And he was not providing the kind of role model that black youth, we always hear, is so in need of (Shanice, shocked at Emile's beating, demanded to know whether she was supposed to try to be like Joe). But such clichéd responses, while clearly part of what Williams had in mind, were insufficient; there was an anger here that lay too deep for words.

The words were vital, though. Williams knows the vocabulary and grammar of contemporary inner-city slang – "chat shit", "bare", "shank" – better than most adults, certainly better than most writers, and that command gave the drama pace and spark. But at the same time, the dialogue remained artificial: too pointed, too non-naturalistic; shorn of the phatic nonsense that sprinkles ordinary conversation, it felt very formal. Ian Rickson's direction took the action out into the London streets, but the script felt stuck in the theatre. The end result was a film that was compelling and complicating in the right ways, defying the bien-pensant shock that seems to hover around the rest of this season – and yet weirdly underpowered. At the end, I wasn't sure how much any of it mattered. Then again, to feel that TV matters at all is, these days, not something you take for granted.