Laurie Sansom steers Muriel Spark's The Driver's Seat to the stage

The Driver's Seat is is a novella that first appeared in 1970, and is here adapted by Sansom himself for its first appearance onstage. Like The Prime Of Miss Jean Brodie, The Driver's Seat looks at an impeccably singular woman. Where Jean Brodie confines herself within the school walls, Lise, the heroine of The Driver's Seat, is a woman in constant motion as she drives to an unnamed Italian city in search of someone who may or may not exist and who might just change her life forever.

"Lise is a mystery," says Sansom. " She's an enigma, and Muriel doesn't tell us very much about what she's thinking or why she's doing what she's doing. There's a mystery at the heart of the story, and the book is all about sub-text. By the time you get to the end, things have been completely turned on their head and you're made to see them totally differently.

"As soon as I read The Driver's Seat I immediately saw it on stage, because there's something essentially quite dramatic going on. I became fascinated by what the story's about - which is chronic loneliness, and how this woman shapes-shifts and changes her personality as she tries to create a new identity."

Sansom admits to a huge love of police and detective procedurals. "I'm a massive fan of The Killing," he confesses, "and The Driver's Seat is a thriller and a detective story, but at the heart of it is this metaphysical investigation into identity, fate and whether we're truly in control of our own lives, or whether there are other things at play that mean we're not."

He read The Driver's Seat while working on The Prime Of Miss Jean Brodie, before which he was barely aware of Spark's work.

"I'd never even seen the film of Brodie," he admits, "and because I didn't know anything about this woman and her work, that's what led me to the play and to this character who has become so iconic. Brodie is the kind of gateway drug into Muriel Spark's oeuvre, and there are so many other cracking books by her that we could have a National Theatre of Spark.

"I think she is underestimated as one of Scotland's genius literary figures, and I think there are many Sparkians, like Ian Rankin, Janice Galloway, Louise Welsh and Ali Smith, who would bang the drum for her. She's such a brilliant modernist writer, and the innovation and the idiosyncrasies of her writing perhaps aren't necessarily recognised, because Brodie is the one that has come to define her to a lot of people."

Sansom approached Penelope Jardine, Spark's great friend who now runs the late writer's estate, with a view to adapting The Driver's Seat. Jardine had seen Sansom's production of The Prime Of Miss Jean Brodie, and liked it well enough to give him the go ahead to explore how to stage a story that is both complex and intimate.

"The book goes to 16 different locations in just 100 pages," Sansom points out, "so it's quite complicated to stage. There are layers of ambiguity running throughout the story, and it's really hard to do ambiguity onstage, so how you create those mysterious layers without confusing the audience is really key. How do you tell the story clearly, but keep it odd and mysterious and enigmatic?"

With this in mind, Sansom has incorporated two hand-held cameras used by the show's seven actors throughout.

"That way we can play with what the audience sees, and also around her you also have a sense of the actors being like detectives watching Lise, studying her and trying to understand her. So in a way the actors are like a reader or an audience trying to understand this crazy woman travelling to all these different places that we don't quite recognise, but which are like a mind map of Lise's world.

"Unusually for a novelist," Sansom points out, "Muriel doesn't tell us what Lise is thinking. You would expect a novelist to be right inside a character's head, but instead she observes her, and remains as objective about her as we do. To try to capture that onstage is not easy."

The Driver's Seat was Spark's favourite of her novels, and it has gained in status over the years. In 2010 it was named as one of six novels to be nominated for the Lost Man Booker Prize of 1970, an award which had been deleted for 40 years after a rule change in the then fledgling competition disqualified the best part of a year's worth of literature from being eligible.

The only previous dramatic adaptation of The Driver's Seat was for a film made in 1974 by Italian writer and director Giuseppe Patroni Griffi, who renamed it for the American market as Identikit. As Lise, the film starred Elizabeth Taylor, who came to the role on the back of her first divorce from Richard Burton, whom she remarried a year later. This rarely seen curio is also notable for featuring Andy Warhol in a cameo role as an English Lord.

"The film's terrible," says Sansom. "It's awful, and Muriel hated it, but if I tell you what she said about it then it would give away the ending."

In this respect Sansom is staying true to the essence of the book in all its weird and wonderful glory.

"It's a disturbing book," says Sansom, "because it addresses violences against women. Muriel addresses this quite a lot in her work, and she talks about satirising and mocking aggression against women, and how that is the best way to deal with it. Rather than make the reader pity the victim, she says the best way is to expose it for what it is and to ridicule it. That gives The Driver's Seat an extraordinary tone. It is about predatory men, so it's creepy and disturbing, but it's also darkly comic.

"It's a creepy road movie in a way, but it says a lot about gender politics as well. When it was written we'd had a decade of free love that had trickled down, and it looks at what the relationships are between men and women after all that, and it asks who really is in the driving seat."

The Driver's Seat, Royal Lyceum Theatre, Edinburgh, June 13-27; Tramway, Glasgow, July 2-4.

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