The final in a trilogy of stories for the Fifth Doctor, Nyssa, Adric and Tegan, the TARDIS team are caught up in a web of assassinations, tax havens and stowaways in the latest monthly adventure, Serpent in the Silver Mask.

The latest tale in the Doctor Who Monthly Adventures is out now.

You are cordially invited to Argentia, the galaxy’s most exclusive tax haven, to attend the funeral of mining magnate Carlo Mazzini. The memorial service will be followed by music, light refreshments, and murder!

Carlo’s heirs have come to say their final goodbyes (and find out how much they’ve inherited) but when a masked killer begins picking them off one by one, Argentia goes into lock-down, closed off behind its own temporal displacement field.

Can the Doctor, Nyssa, Tegan and Adric apprehend the murderer before Argentia – and everyone on board – is forever cut off from the rest of the universe?

More about this tale from writer David Llewellyn, “How did we end up combining Giallo movies – famously gory, often a bit kinky – and charming Ealing black comedy Kind Hearts and Coronets? Well, practicality first and foremost. We had a full TARDIS, so that limited the number of guest actors!

"Then I thought of movies like Dr Strangelove and Kind Hearts…, where one actor plays a variety of roles, and I yelled, “Eureka!” Of course, you’d need someone with considerable acting chops to carry that off, so when Barnaby Edwards (the director) told me they’d cast Sam West as the Mazzinis I was over the moon.”

Script editor Guy Adams lets us know what to expect: “In a delicious slice of Space Giallo from David Llewellyn, our heroes find themselves trapped at a memorial service on Argentia, the galaxy’s most exclusive tax haven. Sealed off from the rest of time, will they manage to stop the Serpent in the Silver Mask before he or she kills again?

“David and I discovered we both shared a love of Italian Giallo movies – stylish thrillers hugely popular in the 1970s – so when I approached him it seemed sensible to turn this mutual love to our advantage. Serpent in the Silver Mask is a blissfully fun murder mystery shot with the gloss and spectacle that the Italians loved to bring to the form. If Mario Bava had directed a version of Kind Hearts and Coronets in space – and now I come to think of it, why didn’t he? – it would have been something like this.”

Serpent in the Silver Mask 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 subscribe to the Main Range in either six or twelve-month subscriptions. Subscribers enjoy a range of bonuses including exclusive extras from behind-the-scenes, up to four exclusive subscriber Short Trips releases, PDFs of each script, and a free Big Finish release.

Coming out next month in the Doctor Who Main Range is The Helliax Rift, where the Fifth Doctor crosses paths with UNIT for the first time. Starring Blake Harrison (from the Inbetweeners) and Peter Davison, it’s another adventure not to be missed!

Daniel Hopkins thought he knew what he was letting himself in for when he joined the top-secret UNIT organisation as its latest Medical Officer.

Racing about the countryside, chasing strange lights in the sky? Check. Defending the realm against extraterrestrial incursion? Check. Frequent ear-bashings from UNIT’s UK CO, the famously no-nonsense Lt-Col Lewis Price? Check. Close encounters of the First, Second and even Third kind? Check, check, check.

But he had no idea what alien beings were really like. Until the day of the Fallen Kestrel. Until the day he met the Doctor.