Before I started writing novels, I wanted to work in the theatre. I acted in plays at school. I directed them at university. I went to shows three or four nights a week, often standing at the back of the stalls, which would cost as little as two pounds. I tried to get into drama school and I applied for jobs as an assistant stage manager, which in those days was a recognised way into the profession. It never worked. I began to see there was something about me that not only didn’t fit in with the world I so wanted to enter, it somehow barred me from it. ‘Ambition, madam, is a great man’s madness,’ says Antonio in Webster’s The Duchess of Malfi, a play I first saw at the RSC in 1971 with Judi Dench in the title role. But it’s accepting that you will never achieve your ambition that can really drive you mad.

Perhaps that was part of the reason why I wrote Mindgame. I was keeping the flame alive.

Mindgame was actually inspired by another play I’d seen in my teens and which had obsessed me ever since. Sleuth by Anthony Shaffer (brother of Peter) was both a parody of Agatha Christie and a completely original murder mystery, as inventive as anything she had ever created. There were only three characters – a wealthy writer, his wife’s lover and a lugubrious detective called Inspector Doppler – but in the space of two acts the play managed to pull off a series of extraordinary surprises, doing things on the stage that had never been done before and leaving the audience gasping. It was a huge hit. It ran for over two thousand performances. It won major awards. It was filmed … twice. To this day, it remains a theatrical landmark.

It goes without saying that there have been attempts to replicate the success of Sleuth, but apart from Ira Levin (Deathtrap), nobody has come close. When you think about it, there’s not a great deal you can do on the stage. Magic and illusion may have a part to play, but so much of theatre is words: people moving about a space, talking to each other. Shaffer broke the physical rules – just as his brother did with Black Comedy, a farce that takes place during a power cut, the stage lights coming on only when the blackout supposedly begins. The trouble is, once the rules have been broken, nobody will be excited when someone else does it a second time. If something is unique, it can’t be done twice.

Even so, it had become an obsession of mine to do exactly that: to write a play with a small cast and a series of twists and turns in the manner of a traditional murder mystery, but using the stage in an entirely new and surprising way. Whenever I found myself between books or TV scripts, I would scribble down ideas and over the years I had completed three plays before I came up with the idea for Mindgame. I had, incidentally, had limited success. One of my works, a one-act play called A Handbag, was performed as part of a local festival. The other two were never produced.