High Society, Regent's Park Open Air Theatre, London

This isn't a musical, it's a mutation. The 1956 movie, starring Grace Kelly, gave us a musical-comedy heroine who did not sing or dance. Bing Crosby as her ever-loving ex-husband, and Frank Sinatra as a reporter who is covering her second wedding (to a jerk) were far too old for their roles. The songs, from a Cole Porter also past his peak, contributed to the dying-embers quality of a movie already steeped in sad irony: Crosby, a real-life drunk playing a reformed alcoholic, had been Kelly's lover; soon she would be off to marry Prince Rainier.

High Society looks even worse compared with its source, The Philadelphia Story. The film version of Philip Barry's play starred Katharine Hepburn, a real aristocrat; Cary Grant, an imitation better than the real thing; and Jimmy Stewart, one of nature's noblemen. The Regent's Park actors must not only compete with our memories of them but struggle with a book, by Arthur Kopit, that lurches about like an old-timer with DTs rather than kicking up its heels in intoxicated glee.

The musical side of the show is also a mess. This 1997 version chucks in tunes that Porter wrote 20 and 30 years earlier, creating a mish-mash that is contrary to the characters' personalities and obstructive to the plot. Though the theme of the story is self-realisation (the haughty Tracy learns to accept her own frailties and those of others; the reporter abandons his self-destructive fascination with the rich), no one thrills us by conveying in song what they could not in dialogue.

Tracy's frosty façade crumbles when she and the reporter, high on champagne, decide to go for a nude midnight swim. But between the thought and the deed there are three musical declarations of passion and self-examination. In that time, surely, nature would prevent what sober reflection did not.

The one essential quality for this show is class. Ian Talbot's fussy, laboured production, with its gruesome servant chorus and champagne served in saucer-shaped glasses, has none. Annette McLaughlin's Tracy is a brassy, scowling fishwife; Claire Redcliffe, as her younger sister, is a squawking pest. Dale Rapley is hangdog rather than yearning as the ex, Hal Fowler limp as the reporter, and Walter van Dyk, as the fiancé, has an appalling Southern accent and a wig whose loss must have made the sheepdog it was taken from very cross. Tracie Bennett, as the reporter's girlfriend, would be quite funny if she didn't pound out her laugh lines like a crazed axe murderess. I was startled by her resemblance to Ida Lupino and asked my companion, "Is she really that old?"

"She is not," he said sombrely. "Fear has aged her."

To 13 Sept (020-7486 2431)