Towards the end of Noël Coward's The Vortex - still ensconced at the Apollo, with Felicity Kendal still tumbling into the maelstrom of the title - a callow 24-year-old ends up yelling at his louche mum: “You're going to be my mother for once, it's time I had one before I go over the edge altogether”. He might be speaking for the teenager at the centre of the play Polly Stenham wrote when, at 19, she was five years younger than the Coward of The Vortex. The differences are that Henry, as he's called, is more parent than son to his impossible mother and that he and his sister are victims of a neglectful father too.

That Face has its prolix and its overstated moments, but it impressed everyone when it launched Stenham's career at the Royal Court's Theatre Upstairs last year. With reason too, since it catches the confusions of an Ab Fab-style family that's clearly been disintegrating since the father, Julian Wadham's Hugh, remarried and absconded to Hong Kong.

Hannah Murray's Mia, his daughter, faces expulsion from school after dorm initiation rites left a 13-year-old in a coma. And Lindsay Duncan's Martha, his first wife, trails woozily round her chaotic bedroom boozing, flirting with the telephone talking clock, making incestuous passes at Henry and cutting up his clothes when she suspects he's been unfaithful.

Is it plausible that an 18-year-old would ditch his academic prospects to look after his awful mother explaining, “She's my life”? Well, Matt Smith (pictured with Duncan) has the emotional intensity to make you buy it, sometimes calling her “Mummy” and sometimes “Martha”; sometimes berating her and sometimes accepting her retchy kisses; and always trying to get her into rehab. This gangling, gawky actor gives a performance to match the excellent Duncan, who is very much the self-indulgent slattern and yet, faced with the chance to stop Henry toppling into the abyss, finds something residually maternal inside herself.

Certainly Stenham comes up with a denouement that, this being 2008, outdoes The Vortex for rawness. The expletives fly as Smith's Henry, dramatising his oedipal agonies by wearing his mother's nightie, rages at his father, his mother, his life, everything. And the conclusion? A surprisingly conservative one, I think. Even highly sophisticated adolescents need their parents. Sane, sensible parents. Two of them.

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