Doctor Who - The Fourth Doctor Adventures: Dethras is now available; a brand new story written by Adrian Poynton and directed by Nicholas Briggs, guest starring Sheila Ruskin (Doctor Who - The Keeper of Traken) and Alistair Petrie (Star Wars: Rogue One):

In the control room of a World War 2 submarine something strange has started to happen. As the ship runs out of control, its crew begin to fall unconscious...

Finding the submarine in the last place they'd have expected, the Doctor and Romana are confronted by a mystery. Once fully populated, there are now only three men on board. And there's now also a chimpanzee.

What has happened to the rest of the crew? What are the strange noises they can hear outside the hull?

And most importantly, who, or what, is Dethras?

Doctor Who - The Fourth Doctor Adventures: Dethras can be bought for £8.99 on Download or £10.99 on CD - or the entire nine releases of this sixth series can be Subscribed to for just £65 on Download or £75 for CD. Next year's seventh series starring Tom Baker and Louise Jameson as the Doctor and Leela can also be Subscribed to, while all five previous sets of stories can be bought individually, or in money-saving bundles. Any of these titles bought on CD will immediately unlock a Download version exclusively to your Big Finish account.

Check out all of the Fourth Doctor stories at Big Finish - including June's Doctor Who - Subterranea, the trailer for which went live yesterday: