The Age of Consent, Bush Theatre, London

Two interwoven monologues, one about the murder of a child in the past, the other showing us a child slowly being destroyed, make up Peter Morris's dread-filled, funny, and perceptive play. Behind the actors, a roll of white paper hangs to the floor and extends beneath their feet; as each one starts to speak, a camera on a tripod clicks and flashes, but the stories, with the stark reality of a series of mug shots, hardly need this arty device to confer authenticity.

Otherwise, though, Edward Dick's production is impeccable, using the actors' stillness to underline the horror of their monologues, as one speaker tries to convince us that he is normal, the other that she is a success.

The character of Timmy is Morris's idea of how one of the boys who killed James Bulger might have turned out. On the verge of release, Timmy says, "I'm not bored any more, but I still try to look it, 'cos there's not much difference between looking bored... and looking rehabilitated.'' Behind the bored looks, of course, is anger, but not at the prison, where he has been educated and taken on outings that he recalls with pleasure. Timmy is indignant and disgusted at the world outside: the rabble-rousing tabloids that call him evil; the shiftless mother and her violent boyfriends; the ugly, hope-killing neighbourhood where he lived.

The targets are predictable ones, but Morris gives Timmy lines that, sometimes rattled out with facile charm, sometimes searching and stumbling, movingly portray this child's vulnerability, that tell us why he always had to spend most of his energy fighting the circumstances of his life or trying to forget them. When, playing truant, he would walk by an abandoned, decayed factory and see "a past that has always been ruined, before you were even born... like machinery can get depressed.''

Throwing away some of the most heartbreaking lines, playing against others with bright, even cocky, eagerness, Ben Silverstone is a wonderfully believable and endearing Timmy. His quickly changing moods, his shock at suddenly breaking down (he pulls his sweatshirt hood quickly over his head, like a child's blanket) make him seem as if he could be any teenager – a thought that is hardly reassuring.

Stephanie's story, by contrast, is entirely fictional and overtly comic. Determined that her six-year-old daughter will provide not only the love but the money Stephanie has never had, she pushes little Raquel on stage and tells her to shove out her "tits'' and smile, smile, smile. Stephanie's narcissism, her genteel speech ("certain intimacies'' for a knee-trembler) and vulgar behaviour are worked expertly for laughs that start to stick in our throats as we realise they align us with those who stand by, condescending and amused, while Raquel's plight becomes more and more sickening.

At the same time, we sympathise with Stephanie, who, like her daughter, is the victim of an oversexed and impersonal society. Katherine Parkinson is good at showing us Stephanie's creamy complacency, but she doesn't fully convey her viciousness. The problem, though, lies more in the script – the comedy of Morris's lines is undercut by their often seeming too clever, too sophisticated, or too old for the character. A minor fault, though, in a stunning evening.