The Dead Eye Boy, Hampstead Theatre, London

Out of sight, out of mind

You couldn't do much better for an image of blinkered optimism. In this play by the much-praised American Angus MacLachlan, Billy, a vacuum-cleaner salesman, demonstrates how his machine will create a healthy environment, unrolling a strip of pale carpet – atop a rubble-heap.

One striking visual metaphor (hardly, of course, an original one) does not, however, make a play. In The Dead Eye Boy, directed by Jennie Darnell, the rubble symbolises the world on either side of Sheila's living-room, but it could also stand for the mess within. The play opens with Billy proposing to Sheila (a consummately convincing Nicola Walker), whom he has met at a group for recovering drug addicts. The deliriously happy couple clearly have only one place to go, and MacLachlan drops them right in it.

The title character is Sheila's 14-year-old son, conceived when she was raped at the same age, and suffering from a birth defect. His open contempt for his mother turns into physical fights that end in rough, sexual play, their only means of expressing affection. While at times he welcomes Billy's influence, he is more often jealous and hostile, repeatedly attacking him until he provokes the final debacle.

The slapping and screaming in the house alternates with vignettes outside: Billy informing the group of his new circumstances ("Thanks for lettin' me share"); Sheila visiting the school psychiatrist with her son, who sullenly tears sheets of paper into tiny pieces, like the character in the Mel Brooks analyst routine – without, sadly, anyone shouting, like Brooks, "Stop tearing up little pieces of paper!'' Purporting to tell us more about the characters, these scenes merely repeat, in an earnest, plonking way, what we already know.

What is more annoying than MacLachlan's leaden dialogue, though, is his phoniness. We're never told why the barely literate Sheila named her son Soren, though middle-class theatre-goers will be able to recognise the allusion to the Danish gloom-merchant, along with the rubble-heap's nod to Beckett. Though the intimate nature of the play presupposes a concern for its wounded characters, they remain unexplored and undeveloped – Billy blandly righteous, Sheila childish and hysterical, Soren flicking between passive and vicious. Soren's isolation and vulnerability are plainest when the couple are wrapped up in each other, sometimes literally: during one sex session, as Billy's shirt is wound round Sheila's head, he tiptoes past them, unseen, and goes out to steal a truck (he is eventually killed in one). The scene may prove comforting to parents and step-parents embarrassed by their own, lesser neglect and self-absorption, but, like the rest of The Dead Eye Boy, it does not show us very much and seems simply voyeuristic.

To 9 Feb (020-7722 9301)