Picking up from the end of Gallifrey V, the sixth series opens with the invasion of a Dalek assault squad as our heroes attempt to save the planet and return home.

Co-producer Gary Russell explains: 'Scott Handcock and l always knew a war was coming to the universe - to each and every universe in fact - and the Daleks' arrival on Gallifrey is one of the triggers. But what do the Daleks actually want? This had to be more than just a run-of-the-mill Dalek invasion story. On top of that - look at those Daleks! Such a thrill to see them on the cover, to see out our final series in style. And it was doubly nice because it gave us the chance to finally drag Nick Briggs into the Gallifrey family properly and give him a chance to make his mark on one of Big Finish's longest-running series!'

Written by Scott Handcock, James Goss and Justin Richards, and directed by Gary Russell, Gallifrey VI stars Lalla Ward as Romana, Louise Jameson as Leela and Seán Carlsen as Narvin, with John Leeson returning as K9 as the saga draws to a close.

Joining them is Juliet Landau - best known to television audiences for her portrayal of Drusilla in Buffy The Vampire Slayer - who takes on a very special role as a future incarnation of Romana... but how she comes to be involved in the story - and her relationship with Romana's second incarnation - remains to be heard.

'Everyone was so excited to be working alongside Juliet,' says Gary. 'The role was always going to be a great one to cast but when we knew we had Juliet aboard, it made it extra-special! Putting aside my long-time fanboy Buffy/Angel geeking-out moments in studio, it was brilliant to discover just how much Juliet immersed herself in the role. Believe me, she'd done her homework - there wasn't a planet or character she didn't know how to pronounce or wasn't aware of the back-story to. She made the days in studio so much fun!'

Juliet will also appear alongside Lalla Ward and Davros actor Terry Molloy in January's Companion Chronicles release, Luna Romana, written by Matt Fitton.

The sixth and final series of Gallifrey audiobooks is available to pre-order now on CD and download. The set will also include an exclusive retrospective documentary looking back at all six series, featuring interviews with cast and crew.