Doctor Who – Red Planets is out now.

London, 2017. Except... it isn't. Berlin, 1961. But it isn't that either. Not really. Not in the timeline the Doctor knows. Something is very wrong.

While Ace tries to save the life of a wounded British spy, Mel and the Doctor must get to grips with the modern day socialist Republic of Mokoshia. For Mel it feels strangely familiar and 'right', which makes the Doctor feel even more uneasy.

Soon, a message from a dark and blood-soaked distant future is on its way... but the Doctor will have to act fast to stop this timeline becoming reality.

And with Ace stranded in an alternate 1961, will saving Earth end her existence?

Writer Una McCormack told us more about this tale: “I hugely enjoyed writing this story. It was a more complex Big Finish script than I’d ever tried before, but I was supported hugely by the script editor, Guy Adams, who helped me achieve a four-part story.

“It helped that we shared a love and enthusiasm for Le Carré and other spy stories, which were the main inspiration for this. The Spy Who Came in from the Cold is a particular favourite. I also wanted something slightly on the feel of the Pertwee story, Inferno, where an alternate timeline is brought to a halt. And of course the centenary of the Russian Revolution was much in the news when I pitched the story back in 2017.”

Red Planets is available now at £14.99 on CD or £12.99 on download. All CD purchases unlock a download option via the Big Finish app and the Big Finish website.

Or you can save money by getting a subscription to the Doctor Who Main Range. When you subscribe you'll get 30% off the price, free specially recorded Short Trips stories, PDFs of the scripts, and extended downloadable extras. You can subscribe for either 6 or 12 releases.

Coming next in the Doctor Who Main Range is The Dispossessed, where the Seventh Doctor, Ace and Mel find themselves trapped in a world unlike any they’ve encountered before…

The Doctor, Ace and Mel are caught in a forever night. After crossing the threshold, a strange world awaits them.

An army of tortured souls. A lift that leads to an alien landscape. An alien warlord, left for dead, and willing to do anything to prolong his life… it’s all in a day’s work for the Doctor.

But when his companions become victims of the desperate and powerful Arkallax, the Doctor will have to do battle in a psychic environment where he must make a choice. Save his companions… or himself.