THIS week is your last chance to see Alan Ayckbourn's fourth production of the year at the Stephen Joseph Theatre, and your car journey from York to Scarborough hopefully will be of pretty much the same duration as the play itself, 75 minutes.

More correctly, No Knowing is a comedy of two halves in the McCarthy auditorium – Knowing Her and Knowing Him – with a brief interval in between for a discussion of what might happen next in the world premiere of this intriguing and trepidatious Christmas comedy.

Ayckbourn's set-up involves Elspeth and Arthur "celebrating" 40 years of quiet, safe, unspectacular, ordinary marriage..."or so most of the guests attending their anniversary party are led to believe".

Knowing her and knowing him as they do, their son and daughter Nigel and Alison know differently in a story of eye-opening revelations presented by a quartet of cast members from Ayckbourn's summer revival of Henceforward, Bill Champion, Russell Dixon, Jacqueline King and Laura Matthews.

"It's back to the very old days when I used to do a lot of shorter plays," says Alan. "This one follows on very rapidly from the other short plays I did this summer for the lunchtime theatre show, Consuming Passions.

"I've always felt that the [SJT] theatre needs some sort of theatrical presence over the Christmas period for those who have no convenient child to bring to a show as it can be a bit miserable sitting on your own during a children's show."

Hence the SJT host is playing host to Nick Lane's wonderfully witty and delightfully daft new adaptation of Pinocchio in The Round, while Ayckbourn's No Knowing takes over upstairs in The McCarthy.

York Press:

Russell Dixon as Arthur, left, Bill Champion as Nigel, Laura Matthews as Alison and Jacqueline King as Elspeth in Alan Ayckbourn's No Knowing. Picture: Tony Bartholomew/Turnstone Media

Both halves open at Arthur and Elspeth Throkes's 40th wedding anniversary party in August at their semi-detached suburban family home, Elspeth giving her speech in Part One: Knowing Her; Arthur responding in Part Two: Knowing Him. What follows in each half is a flashback, first to Nigel's urgent chat with his father two weeks before Christmas the previous year; then to Alison's equally urgent discussion with her mother a week later.

"We see the marriage from Arthur's point of view and Elspeth's point of view and we come to see the truth behind their slightly anodyne speeches the next summer, and because I wrote it for Christmas it does have quite a positive ending, which is rare for me!"

You should note here that there is still a sting in the tale's final line that suggests any positivity could be as shortlived as the promise of peace between the warring Montagues and Capulets in Shakespeare's Romeo And Juliet.

Ayckbourn's play asks how well you can ever know your partner? "As Arthur says in his speech, 'I married her at 23; how could I possibly know everything about her at that age?'," he says.

No Knowing is not the first Ayckbourn "Christmas play". "A Christmas play is a great excuse to get a whole load of people who don't like each other into a single space and watch them tearing each other apart, like I did in Season's Greetings and Absurd Person Singular, which was set over three Christmases that got progressively worse," he recalls.

Thankfully, Ayckbourn family Christmases in Scarborough are far removed from the fractious gatherings he depicts. "We do all get along and enjoy each other's company," he says.

As for Christmas presents, "The nicest presents are the ones you least expect," suggests Alan, a self-confessed lover of gadgets.

Alan Ayckbourn's No Knowing runs in The McCarthy, Stephen Joseph Theatre, Scarborough until Saturday; performances at 3pm and 8pm, today and tomorrow, and 8pm, Saturday. Box office: 01723 370541 or at sjt.uk.com