On set for Doctor Who's two-part finale: The Time Lord faces a final Twist

It’s July 2023 in Bad Wolf Studios, Cardiff, and as Radio Times looks on, there’s a certain tension in the air. After eight months of filming the series, cast and crew are tired. The days are long and there are limited shooting days left to get everything in the bag before filming wraps up for this year.

"In this final block there is no more time," says director Jamie Donoughue during a brief break. "The directors of previous episodes, if they had little bits to pick up, they could have jumped on with one of our shoots. But once we finish shooting, we finish shooting. We really are up against it. There’s huge pressure, but that’s what I love."

The two-part conclusion, penned by showrunner Russell T Davies – starting with The Legend of Ruby Sunday and concluding next week with Empire of Death – isn’t just the end of Gatwa’s first season. It also puts a cap on the first year of Doctor Who’s big new gamble, teaming up with streaming partners Disney Plus to turn the show into the kind of big-budget, international crossover hit it has always felt a hair’s breadth away from being.

"We want to end on a bang like we’ve never seen," says Donoughue. "This finale is like a huge feature film. I think a lot of people are going to be shocked – if I can pull it off. Hopefully, I will."

Well, we’re about to find out. This week, after six episodes of wild adventures through time and space, Gatwa’s Doctor and best pal Ruby (Millie Gibson) land the TARDIS on present-day Earth, determined to solve the mystery of the strange woman who keeps appearing in the background of their adventures.

Played by actress Susan Twist, she has appeared in every episode thus far in a small (and different) role – but now she’s centre stage, this time as a shady tech billionaire called Susan Triad. But is she friend or foe? And what does any of this have to do with Ruby’s long-lost mother, who abandoned her 18 years ago?

"I know all of Ruby’s secrets!" 19-year-old Gibson tells RT a year later. "Ruby goes through a tricky arc. She breaks your heart a little bit. I obviously know how it ends in this season – but I don’t know how it ends next season."

The rest of the cast and crew also remain tight-lipped – after all, in a series built on surprises and cliffhangers, secrecy is paramount. "There was an action scene where prop guns were used and fake bullets," offers 15-year-old guest star Lenny Rush, who plays Morris, a new scientist among the Doctor’s old friends at UNIT (the Unified Intelligence Taskforce). "That was such a cool experience."

"I can tell you nothing!" laughs returning 1980s companion Bonnie Langford, now teaming up with Gatwa and Gibson for this latest adventure – the 'Three Amigos in Space', as she describes them. "I get to ride a Vespa through London. That’s about it."

On set, only specially approved members of the crew with colour-coded lanyards are allowed to take photos. Everyone working on the show has also been warned of fans (some of whom have stood watching public filming for 12 hours at a time) developing clever tricks to talk information out of them. Codenames have been used to protect the identity of the episode’s villains.

While watching filming, we’re also sworn to secrecy – one jaw-dropping set we explore is completely off-limits for discussion. Another set we visit – dubbed 'The Time Window' – plays a key role in the final episodes and speaks to the new scale of the show and its expanded budget. It’s a huge facility full of buttons, levers and screens (many of which actually work), all looking out over… well, we can’t tell you that. But it’s impressive, and still probably the most humdrum bit of design in a finale full of huge builds.

"When I was in the TARDIS,” laughs Langford recalling her first stint on the show back in 1986, "we had paper plates on the wall and a hat stand! Yes, it’s on a grand scale. Yes, we’ve moved on. Yes, the world has changed – but Doctor Who hasn’t lost the essence of what it was. I think it’s just moved with the times."

And this finale is just the beginning. Gatwa is back in the TARDIS at Christmas (with guest star Nicola Coughlan) and then accompanied by Gibson and new co-star Varada Sethu for a second season of adventures next year, which have already been filmed.

On another set visit some months later, we glimpse whole new worlds, spaceships and buildings being constructed from plywood at vast scale. By now, those sets will have already been completed, painted, filmed on and dismantled. The march of Doctor Who’s expensive new era continues.

But for now, cast and crew wait with bated breath to see how viewers react when all their top-secret filming is finally aired to the world. "Oh my God, the fans who love to pick out every single detail are going to have a field day," says Gibson. "They’re going to rewatch and rewatch and find something new. Even I do that. When we were filming, we were like: 'Oh, that’s what that was for!'"

"It’s jam-packed," Gatwa adds. "Russell is so great at creating a world." We'll all just have to wait and see whether his Doctor had enough time – and takes – to save it.

Doctor Who continues on Saturday 15th June on BBC iPlayer and BBC One. Previous seasons are available to stream on BBC iPlayer.

Check out more of our Sci-Fi coverage or visit our TV Guide and Streaming Guide to see what's on tonight. For more from the biggest stars in TV, listen to The Radio Times Podcast.