Peter Capaldi’s final episode of Doctor Who this Christmas will feature Pearl Mackie as Bill Potts and be called Twice Upon a Time, it was revealed this evening (23 July) during a cast panel at San Diego Comic Con. Viewers will have to wait until Christmas to discover exactly how Bill, who will appear throughout the episode, makes her return.

Now that the Doctor and Clara have established a dynamic as a partnership of equals, they’re relishing the fun and thrills that all of space and time has to offer. Tangling with ghosts, Vikings and the ultimate evil of the Daleks, they embark on their biggest adventures yet. Missy is back to plague the Doctor once more, the Zygons inspire fear as they shape-shift into human clones, and a new arrival moves in cosmic ways.

The Doctor returns, alongside newly weds Amy and Rory, to face monsters and mysteries and adventures all across time and space. Together they find themselves in sixties America, battling the invasion the world forgot, then aboard a pirate ship on the high seas of 1696, to solve the mystery of the Siren. In a bubble universe at the edge of reality, the Doctor meets an old friend with a new face.