Hilda, Hampstead Theatre, London

This play, by the French-Senegalese writer Marie NDiaye, focuses on a solipsistic obsession that masquerades as progressive philanthropy. In the guise of wanting to make a friend and equal of her new nanny-cum-cleaner, the chic, upper-class, inexorable Mme Lemarchand (Stella Gonet) decides to confiscate Hilda from her odd-job-man husband Franck (Bo Poraj) and their children.

Cracks in the employer's left-wing credentials soon show when she congratulates herself on not taking the easier path of hiring one of those abjectly grateful foreign women who will do anything (even service the master) because they're terrified of being deported.

Her charitable project with Hilda (dressing her in stylish cast-offs, cutting her hair, taking her on cultural excursions) steadily reveals itself as a perverted, semi-erotic exercise in possession - creating a slavish substitute to compensate for her own inadequacies as a mother. And all the while, she is trying to seduce Franck when she makes her monthly visits to pay him a portion of Hilda's wages.

The norm in fiction is to demonise nannies (because of our guilt at off-loading parental responsibilities), so it's refreshing that the vampire and victim roles are reversed here. For a while, too, there's black comedy as Gonet's Madame prattles on and on in her impermeably self-centred way.

And, though it can muffle the sound, there's an unsettling psychological aptness to the striking design for Rachel Kavanaugh's production. The Lemarchand home is presented as a revolving cage-like glass-and-steel cube, in which Madame looks suspiciously like one of the toy ballerinas trapped in the musical boxes she collects.

However, I soon lost patience with this piece, which betrays both its radio origins and its debt to the claustrophobic artifice of Genet's The Maids. Initially, it adds to our sense of Madame's overpowering resolve that Hilda is an unseen presence. That she remains so becomes increasingly comic - an acknowledgment that, without this convention, the credibility of the title character's swallowing-up would collapse.

The drama, sharply translated by Sarah Woods, consists of lopsided conversations between the glum husband and his wife's kinky captor, which provoke niggling, common-sense questions - such as, why doesn't he just call the police and have Madame certified?

To 6 May (020-7722 9301)