You can’t say that writer Ian Winterton doesn’t offer value for money. There are enough ideas in Sherica to provide material for a TV series.

And all of them are good. The admission into a posh grammer school of pupils from a less privileged background gives rise to conflict. Katie (Ruth Middleton) is called to the school after her bright but aggressive sister Natalie (Nicola Stebbings) gets into a fight with borderline sociopath Douglas (a remarkable professional debut from William Hutchby).

This gives the amoral Douglas the opportunity for blackmail as Katie works in the sex industry under the name 'Sherica' and her clients include him and Michael (Oliver Devoti) a teacher married to Holly (Katy Slater).

In such a crowded plot contrivances (such as Douglas getting far too many chances to gather evidence) are inevitable. However the characters have a brutal credibility. The centrepiece is a marvellously staged confrontation between Holly and Katie.

Middleton gives a heartbreaking performance as a woman who has sacrificed so much and lives in constant fear that it is not going to be enough. Slater’s nicely ambiguous approach leaves unclear whether Holly believes her actions are in the best interests of Natalie or intended to punish her husband.

Social awareness runs through the play. Being from wealthy backgrounds Douglas and Michael are accustomed to avoiding the consequences of their actions whereas the blameless but skint Natalie is aware that her future is bleak. Festival organiser David Slack goes beyond a comic turn to show the backbone in his hard-working headmaster.

Director Trevor MacFarlane makes a virtue of necessity and uses the theatre in the round to achieve the rapid changes of scene needed to fulfil the complexities of the plot. He still has an eye for detail. Stebbings’ convincing Yorkshire accent marks Natalie as an outsider.

Sherica is a powerful and challenging play that ends just as it is getting really interesting. The possibility of a second act to fill in the fates of the characters ought to be examined.

- Dave Cunningham