Homophobic murder, sexual confusion: this sort of thing never happened in the Oxo family. Lynda Bellingham, mother superior of that cosy televisual domestic world for so many years, plays a mum with far greater concerns than lumpy gravy in Philip Ridley's unsettling but sometimes frustratingly under-involving, two-hander.

This particular River, which premiered at Hampstead in 2000, starts deep and gets deeper, as both characters are peculiarly confessional right away. With no time for a gentle emotional warm-up, we struggle to immerse ourselves as fully as we would like in the repercussions of the murder of 33-year-old homosexual Vincent.

Hounded by the prejudiced taunts of the neighbours on her Bethnal Green estate, Vincent's mother Anita (Bellingham) has been forced to move to a new flat. Here she waits, in an almost furniture-free room, with only a bottle of gin for solace. Sixteen-year-old Davey (Mark Field), who has long lurked outside, has finally been invited in. It was he who found Vincent's body, he says, him and his fiancee.

The final destination of the piece is clear from 10 minutes in but as Ridley handles so adeptly the accretion of layers of detail, it makes the journey worth following. Moments of black humour and blacker horror sit side by side, as Davey offloads the knowledge that has been burdening him onto the one person who is desperate to hear.

Bellingham, who paces about in heels so spiked they could take an eye out, is tremendous as a woman who, despite a valiant struggle, hasn't freed herself from every final shackle of inherited family bigotry. For much of the time Anita is contained, jocular even, but when she cracks, it's with some of the most wrenching onstage tears I have ever seen. Every smudge of that mascara is earned.

Field is suitably edgy, although he never manages to pull into complete cohesion the range of complexities that Ridley has given Davey. Nonetheless, an impressively abrasive West End night.

• Until 17 November. Information: 0870 060 6632; www.theambassadors.com/ trafalgarstudios.