What a remarkable, bright young thing Polly Stenham is! After her precocious debut at 19, with the award-winning That Face, this second play confirms a startling, theatrical promise, though it returns to the terrain of the first.

Again teenagers from affluent backgrounds are exploited or deserted by inadequate, neglectful parents — disturbed mothers in particular. Again Stenham shows a flair for shock-tactics — quite psychologically convincing ones too. Awful burdens are born by unfortunate children. The humour turns dark.

Tusk Tusk’s materfamilias has gone missing, in contrast to the daughter-loathing mother in That Face who took to excessive alcohol and sex with her adolescent son. Her three offspring — seven-year-old Finn, played by the astonishingly assured Finn Bennett, Toby Regbo’s superb Eliot, aged almost 16 and his slightly younger sister, Bel Powley’s worldly Maggie — are discovered in a smart, open-plan living room. Loads of packing cases are haphazardly scattered around. A kitchen sink, that long-lost, almost mythical Royal Court appendage, forms part of an opulent unit, in which nothing is stored apart from rows of home-made jam. And apparently nothing can be cooked
The kids subsist on Chinese take-aways, prawn-crackers and cider. An air of mystery and unease engulfs them. Jeremy Herrin’s assured, dynamically acted production intensifies the mood. Why is there no concern about their mother’s absence? Something crucial is concealed and Stenham never properly explains why.

Meanwhile rubbish piles up and up. Finn, who decorates himself in stripes of lipstick, sleeps under a table. They all stay awake at night and slumber by day. When Eliot disappears one morning, only to bring back a girl — whom Maggie wittily dismisses as if she were a hired tart — it grows clear the teen-agers prefer self-contained closeness and evasion of home-truths.

There are faint but distinct echoes of William Golding’s Lord of the Flies (Eliot’s red Indian call in particular) and Ian McEwan’s The Cement Garden, where kids on their own turn anything from primitive to strangely alienated. Eliot and Maggie talk cool, in sharp, sophisticated blasts of jaunty humour and cynicism — they seem a bit old for their tender years. And adorable Finn sometimes sounds as if his mind were twice as old as his actual years. It is only when he is cut by glass and obviously needs medical aid that Stenham lets slip the play’s secret, revealing just what the kids fear if they hand themselves over to authority. The revelation is not that surprising and Stenham, despite engendering bleak amusement from the spectacle of these kids anarchically making do, fails to develop a powerful enough plot-line. It is only after two adults — friends of the mother — make a late, surprise appearance that Tusk Tusk takes wing.

Thanks to the closing scene, when vituperative Eliot turns upon his mother’s secret, two-timing lover — and Maggie makes an unbelievable confession, Stenham manages to brings this dark comedy of wrecked family relations to a riveting conclusion.
Information 020 7565 5000. Closes 2 May. www.royalcourtheatre.com