This is a Doctor Who story with a difference, as the Doctor steps aside and the companion takes centre stage in this psychiatric drama. Louise Jameson gives a star performance as Leela in The Crowmarsh Experiment, out now.

We asked writer David Llewellyn about the inspiration for his tale: “By sheer coincidence I was born about 3/4 of the way through Invasion of Time's original run on TV, so I started thinking about what it would be like to literally take Leela out of the series; for her to find herself in London in March 1978 and be told that her adventures with the Doctor were all a fantasy.

“Part of that probably came from reading too much Philip K Dick in my teens, especially We Can Remember It For You Wholesale (aka Total Recall). Even the 1990 movie hints (pretty strongly) that everything is happening in Arnie's head, which gives the film's ‘happy’ ending a really bleak twist, and that always appealed to me.

“The important thing was to try and make the scenario as convincing as possible. It either had to plant a seed of doubt in listeners' minds (what if it really was a dream?), or at least make the emotional drama within the Crowmarsh world harrowing for Leela. I've written for Leela before, but it's been the mature, worldly-wise Leela of Gallifrey. I wanted to push her, and see what happens if she starts losing some of her identity. What would she do if you offered her a ‘normal’ life?

“Tonally, the major inspiration was the Hammer House of Horror episode The Two Faces of Evil. I remember watching it on a family trip to East Yorkshire during the Great Storm of 1987. I was nine years old, and while we were watching it, the wind was howling and nearby trees were scratching at the windows. I didn't sleep properly for a week!

“As a kid, it was the stranger in the yellow mack with his creepy fingernail that scared me. Watching it in my 30s, it was the scenes of Anna Calder-Marshall in the hospital. They're genuinely nightmarish, claustrophobic and paranoid. I hope The Crowmarsh Experiment feels a little bit like that!”

Critics have loved this very different Doctor Who story: “Overall, The Crowmarsh Experiment is the type of story that Big Finish rarely does, but when it does it, it does it right. If you’re looking for an existential rollercoaster ride, this is the release for you.” says Gallifrey Archive.

Blogtor Who praises the ensemble: “Boasting a strong cast, with the likes of Dan Starkey, Julian Wadham and Cathy Tyson joining Baker, this is most definitely Louise Jameson’s time to shine. She reminds us that Leela is much more than a savage in skins; she’s a complex character that both the TV series and the audios recognise.”

And particular praise has been given to Big Finish favourite, Louise Jameson: “This shows through most clearly in the set’s standout story, The Crowmarsh Experiment by David Llewellyn. Jameson navigates not just the disconnect between Leela’s new surroundings and her memories but also the emotional impact of being introduced to children she can’t remember and a husband who lives in her memory all too deeply. Jameson’s performance here stands with her role in last year’s War Doctor finale as her finest hour for Big Finish.” (from We Are Cult)

You can purchase The Crowmarsh Experiment as an individual download at £8.99, or with three other adventures in The Fourth Doctor Adventures Series 7: Volume 1, a 4-disc slipcover box set, priced at £23 on CD and £20 on download.

Or you can save in a subscription and get Volumes 1 and 2 of Series 7 at £45 on CD or £40 on download.