There are moments in some of Caryl Churchill's plays that are so bizarre and theatrically audacious that you cannot be sure if you actually saw them, or nodded off in the middle and dreamed them up.
In the terse war play Far Away - also showing as part of the Crucible's grand Churchill retrospective - that moment occurs when a silent parade of extras shuffle through in extravangant hats. In Cloud Nine it happens when a glitter ball descends and the cast interrupt a finely nuanced comedy of sexual mores to break into a disco routine.
Cloud Nine sets out as what appears to be a colonial satire about a khaki-clad governer in the days of empire: yet all is subject to one of Churchill's vigorous shifts of the casting wheel so that the black servant is white, the governer's wife is a man, his son a girl and their daughter a doll. Then they all swap roles and genders after the interval.
In the hands of a lesser writer it would be intolerable and - to be honest - there are passages that, groundbreaking though they were 20 years ago, have the faint whiff of a contrived workshop about them today.
Nevertheless, Anna Mackmin's intelligent revival smooths out the play's capriciousness and highlights its beauties. It features an absolutely glorious performance from Lucy Briers. But though Cloud Nine was undoubtedly theatrical dynamite - blasting the way for so much that was to follow - one cannot help but wonder whether we are looking back into the empty hole.
· Until June 19. Box office: 0114 249 6000.
