Fantasy lives are probably more common than most of us would like to admit. With Woman in Mind Alan Ayckbourn explores what happens when wouldn't-it-have-been-wonderful-if... jars against life-as-it-really-is. Susan is a wife and mother, who we meet in the aftermath of a garden accident (she knocked herself out tripping over a rake) while she is being attended by a doctor.

Then her family – still-gallant husband, loving and attentive son and daughter – materialise. Or do they? In which garden are we? Who are the other members of the household? Is there another son, one sucked into a cult? Ayckbourn subtly weaves us in to the dual tapestry of Susan's mental existence as she seeks to balance fiction and fact.

It's not an easy play for either the cast or the audience, and it has one of the most ambiguous of all of Ayckbourn's open endings. As always, there is much at which to laugh – and Catherine Lomax's production allows that its full spate – but put yourself in Susan's shoes (into her mind, if you will), and it all becomes much darker.

Angie Smith gives a beautifully-nuanced performance as Susan, letting us laugh out loud at (as well as inwardly cry with) the character. You can also sympathise with Tim heath as the vicar, Gerald, bogged down with a parish history pamphlet. As the doctor, Ian Houghton presents an endearingly clumsy practitioner drawn perhaps too closely to his impromptu patient.

There's something unsettling about Michael Humphries' set. Stage left is all realism; stage right has an amateurish appearance with steps veiled unconvincingly in a green floor-cloth. This side of the set is largely the province of Marc Bannerman as Andy, Caroline Rodgers as Lucy and Chris Clarkson as Tony. We also meet Susan's dour sister-in-law Muriel (Faith Hanstater) – never invite her to cook you a meal! – and Rick (Andy Haig) – a springer of surprises.

Lomax's production is the first in what is hoped to be a series of home-grown professional stagings of plays at the Gordon Craig Theatre. It's a bold choice for the start of this programme, but one which deserves to succeed. Audiences do like to be entertained. They also like to be challenged.