I will hold my hands up here and say that I am an unabashed Agatha Christie fan. As with many people, she was my introduction to crime fiction and I recall carrying armfuls of her books from the local library and working my way through them at a rapid pace.

I’m aware of the criticisms levelled at her, most of which could be applied to every other writer of her era, and accept that not all her novels are masterpieces – but few authors command a plot as well as she does.

You can imagine how excited I was when I heard about Upstairs at the Gatehouse’s production of ‘Where is Mrs Christie?’, based around the 11-day disappearance of the celebrated author & playwright in 1926. I’ve actually stayed at the hotel where she was, eventually, found – The Old Swan, in beautiful Harrogate – making this play even more meaningful to me.

Upstairs at the Gatehouse is a wonderful theatre pub in Highgate that seats around 100 and provides the perfect backdrop for this one-woman play, which takes place in Agatha Christie’s drawing room. It begins in 1958 with our heroine, played beautifully by Liz Grand, getting ready to go to a party celebrating the sixth anniversary of ‘The Mousetrap’, already the longest-running play in the West End.

Clad in twin set and pearls, Agatha reads us a somewhat barbed telegram of congratulations from Noel Coward. It’s at this point that the 68 year-old Agatha, defiantly stout and distinctly middle-aged, begins to reminisce, casting her mind back to that defining moment in 1926: “the worst mistake of my life”. But how on earth did this event come to pass?

Agatha, we learn, had married her first husband, Archie despite her mother’s reservations (Archie had no money and this had been a whirlwind romance). Initially, life was idyllic – and Archie returned home safely from the Great War; their daughter, Rosalind, was born in 1919 and subsequently Archie found a job in the City. Cementing this contentment, in 1920 Agatha was offered a five-book deal by Bodley Head.

It’s painful to watch the 1958 version of Agatha as she mulls over the impact of her literary success upon Archie. In a twist that will echo with many women today, nearly 100 years later, Archie begins – slowly but surely – to begrudge his wife’s success. With sadness etched upon her face, Agatha describes how her husband began to belittle her. She fights back – this is no sob story – but, ultimately, “I loved him”.

Cliché after cliché follows: Archie joins a golf club and begins an affair with their mutual friend, Nancy Neele, with Rosalind siding with her father during her parents’ rows. Archie’s jibes continued, with a particular focus on Agatha’s “inability” to lose weight, post-pregnancy – and her “lack of willpower”.

Witnessing the confidence seeping out of Agatha is heart-breaking. Increasingly successful, at home she bends to her husband’s will and in 1926 they buy a large house near Sunningdale Golf Club which they name – ring any bells? – ‘Styles’. And then, suddenly, Agatha’s mother, to whom she has always been incredibly close, dies. How much that event influences what follows is left for the audience to decide – but on 3^rd December 1926 Agatha and Archie have “the row that would change our lives forever”.

Of her sudden disappearance Agatha tells us “I just wanted him to see sense”. At long last, Archie had announced that he was leaving her for Nancy, his parting shot “Our marriage is a sham”. We do, in fact, believe Agatha when she tells us, stutteringly, that she couldn’t have foreseen the impact her subsequent actions would have upon them – yet, as she frankly admits: “The die was cast”.

One of the elements of this play that I most enjoyed was how it interspersed the present day (1958) with news bulletins from 1926 – and nowhere is this more effective than in the latter scenes, when we are treated to snippets of the BBC’s reporting of Agatha Christie’s disappearance, from the initial alarm when her car is found abandoned in Surrey to the growing belief that foul play has occurred. How different today’s world is: in this era of social media it’s difficult to imagine any celebrity escaping the public gaze for more than 24 hours. Yet, Agatha Christie could and did disappear for eleven consecutive days. “I wanted to cause Archie worry – and make him realise that he wanted me back”, a clearly distraught Agatha tells us.

What the nation’s favourite crime author hadn’t counted on was Archie himself becoming a “person of interest” to the police. They’d been told by one of the couple’s maids that Mr and Mrs Christie had had a “massive row” before their mistress disappeared; hardly surprising, then, that all of a sudden Archie found himself helping the police with their enquiries.

After she was found alive and well in Harrogate, Agatha Christie stuck firmly to her story of amnesia. This play, while treating her sympathetically, takes a pragmatic approach to those high-octane days. Yes, Harrogate was the soul of discretion and protected its latest, highly-recognisable resident in a way that London wouldn’t have. Yes, Agatha checked into The Old Swan as Mrs Teresa Neele. And yes, mail for Agatha arrived at the hotel having been redirected there several weeks previously. Reader: make of that what you will.

As Agatha Christie will have known only too well, the truth will always out – and after the hotel’s resident band and one of its chambermaids report Mrs Teresa Neele to the police, Archie and “half of Fleet Street” descend upon the famous spa town. We cringe with Agatha as she recalls the moment when she is “reunited” with her husband – and the reaction of an unimpressed police force.

It’s unlikely we’ll ever know the full truth behind what happened during those fateful eleven days. However, this play attempts to find out in a way that is both touching and humorous and I can’t help feeling that the best-selling author of all time would appreciate both its treatment of her – and the fact that, all these years later, we still care.