Primadoona, Gilded Balloon

Gnarls Barkley's "Crazy" is playing as Doon MacKichan, star of Smack the Pony and Brass Eye, gangles on to the stage. It's grimly apt for this, the tale of Doon's downward spiral in the decade since her Emmy triumphs.

She picks up a red telephone. "Hi God. Just wondering how many more bad things are going to happen?" These "bad things" include her father dying while she was doing a farce in the West End, her 15-year marriage falling apart just as she gave birth to a third child, her career nose-diving and, above all, her young son being diagnosed with leukemia.

All of this doesn't stop the show from being very funny – for the first half at least. MacKichan is a gifted character actress and a lithe comic performer. Valentine's Day is an opportunity to do "the single girl's dance with cava" in her kitchen while a first date is played out entirely in mime. She's not in the least afraid to make a fool of herself as a set of increasingly strained voiceovers for Ibiza compilations, sat navs and gynaecological lotions shows.

In the second half, the show takes a more serious turn. The story of her son's illness is sensitively told, with the dramaturgical help of Bryony Lavery: a quietly desperate tale of parents crying in car parks and chopping vegetables in hospice kitchens, of baffling treatment options and a disintegrating marriage. At the end, MacKichan emerges triumphant. It's a joyful finale to a piece which at times teeters dangerously on the brink of theatre as therapy.

To 30 August (0131 622 6552)