It's the darkest hour for a most faithful companion, in the penultimate story of The Fourth Doctor Adventures Series 4, released today.

Doctor Who: The Fourth Doctor Adventures – full cast audio dramas, starring Tom Baker, effortlessly recreating the trademark wit, wisdom and humour of his incarnation of the legendary Time Lord. Paired with his faithful companions, it's a nostalgic trip back to the 1970s in stories designed to capture the distinctive flavour of that era.

There are dark skies on Krelos… and something gigantic is descending.

Meanwhile, the Doctor and Leela set off for some fishing in the mountain pools of Krelos. K9 has interfaced with the TARDIS and has reactivated the architectural configuration from the days of the Doctor’s second incarnation. In passing, the Doctor notes it could do with a good clean. And there’s a familiar piece of material snagged on the console.

Far up the mountain, an aged explorer is in trouble. Will the Doctor and Leela be able to save him and his planet? And what is it that K9 has discovered in the TARDIS?

Doctor Who: The Fate of Krelos, a new story by Nicholas Briggs, stars Tom Baker, Louise Jameson and John Leeson, and it’s available to buy and download today.

Join us in August for the climactic adventure of The Fourth Doctor Adventures Series 4 – Doctor Who: Return to Telos, where an old companion, older enemies and a deadly new threat await the Doctor...

You can catch up on the series so far today on the Big Finish website.