Jo Smith arrives at her local theatre for an audition with the director Vyvian Jones, but it transpires that she has actually been invited there by Beverley, Vyvian's twin brother, who wants her to impersonate her own twin sister Fiona in order to scotch the rumour that Beverley has slept with Fiona. (He has, but doesn't want Vyvian to tell his fiancee Cheryl.) Jo reluctantly accepts this unusual acting job and pretends to be Fiona to Vyvian. But then the real Fiona arrives and thinks Vyvian is Beverley - and then Vyvian, who is a member of the local Sons of Satan Association, takes Jo captive to use as a human sacrifice - and then...Only the intervention of a policeman, Janet Jones (Beverley's and Vyvian's identical younger brother) can save the day as matters get more than a little confusing...One actor and one actress play all the Joneses and Smiths respectively in this fast-moving madcap comedy of multiple mistaken identity.