Unsuspecting Susan, King's Head Theatre, London

"I'm the only female campanologist this side of Andover," breezes Susan, the solo character in Stewart Permutt's new monologue. But as the play's title - Unsuspecting Susan - all-too-explicitly flags, it's the alarm bells in her life that she is refusing to hear. This fiftysomething divorcée, a firm Home Counties type, is talking to us from her drawing-room in the village where she lives with her two dogs. She's played by Celia Imrie, the immortal Miss Babs in Acorn Antiques, and what with the Victoria Wood connection and the monologue form, you feel that you're in for a camped-up parody of an Alan Bennett Talking Head.

The various ingredients are all in place. There are those tell-tale discrepancies between what she intends and what we actually hear in the remarks she makes. When she reports that "Mummy had this wonderful knack of making everyone feel equal", you fancy that people from all backgrounds were flattened in the wind of Mummy's condescension. There are the wilful blind spots, here rather crudely registered. "One day I know he's going to make some girl very happy," insists Susan of her mentally disturbed son, Simon, who is flat-sharing with Jemal, a young Egyptian. There are those things that are left, betrayingly, unsaid.

The result, in Lisa Forrell's adroitly paced production, is often highly entertaining, and I laughed out loud on several occasions. What the piece does not have, however, is the radical ambiguity ofthe best Bennett monologues (such as A Woman of No Importance), where the speakers' characteristics can be seen as deeply irritating yet oddly courageous, or admirably stoic yet selfishly destructive.

Then a police raid on her house brings home to Susan that there was more she did not suspect about her Simon than his sexual leanings. Because of his mental vulnerability, he was targeted by an Islamic terrorist group, using Jemal as their recruiter, and brainwashed into becoming a suicide bomber. He has just died in a blast in London restaurant that killed and maimed others. Having been deliciously camp and in-on-the-joke to just the right degree, Celia Imrie then takes you with great sensitivity into the dazed grief of a woman whose self- protective instincts makes her concoct an unpleasant political rationalisation for Simon's actions. Spat at and ostracised, with only a gin-sodden female crony remaining loyal to her, the character demonstrates immense fortitude.

The last words of the monologue are "After all, I'm not to blame - am I?" But while it has been hinted throughout that Susan was scornfully dismissive of her ex-husband, ignorant of the ways in which the father and son tried to maintain some contact despite her, she can scarcely be held accountable for Simon's schizophrenia, a condition that is genetic in origin. So Susan's vices never come across as the flipside of her virtues, leaving the play without that doubleness and concentration of effect you find in the finest monologues.

To 15 June (020-7226 1916)