Russell T. Davies and Ncuti Gatwa tease Varada Sethu’s new companion in Doctor Who — and Millie Gibson’s return.

Davies says that Belinda Chandra is unusually resistant to the Doctor’s lifestyle: “Why am I a prisoner on this runaway train? Take me home!

Ncuti Gatwa’s Doctor has a new companion in the upcoming season of Doctor Who—and unlike most of his other co-leads, she really, really doesn’t want to be there.

The sci-fi adventure’s season premiere, which hits BBC and Disney+ on April 12, sees Varada Sethu’s hardworking nurse Belinda Chandra whisked away to a bizarre robot planet with a mysterious connection to her past. Right from the start, it’s clear that she just wants her life to go back to normal.

“We’ve had a year of Millie Gibson as Ruby Sunday, who was gorgeous and lovely, but kind of in love with the Doctor, wide-eyed and loving it,” showrunner Russell T. Davies tells Entertainment Weekly. “I think I’d be much more like Belinda in real life thinking, ‘Who is this? Why am I shackled to a madman? Why am I a prisoner on this runaway train? Take me home!’ She’s very much aware that people die around the Doctor. It’s trouble.”

Despite their wildly different lifestyles and philosophies, Varada and the Doctor immediately establish a lively rapport reminiscent of the show’s strongest companion-Time Lord combos, thanks to both actors’ enthusiasm and slightly antagonistic chemistry. “I was in awe of her performance every day,” Gatwa says of his new co-star. “Varada is just an incredible actor. Incredibly grounded, so truthful, and gives so much — to the text, and to other actors. It’s just incredibly enriching to work with.”

The actress isn’t exactly a Doctor Who newcomer, though — she previously played a different character, Mundy Flynn, who faced off with Gatwa’s Doctor on a war-torn planet in the episode “Boom” last season.

“When Varada came in to do one episode last season and I loved her in it, I was sad that we’d never see her again,” Davies says. “Bear in mind, when we all sit in the edit of these episodes, we must watch them 50 times — every edit, every dub, every final mix, every grade. And still, after 50 viewings, I was watching her thinking, ‘God, she’s good. I love her!'”

The preliminary casting process for Belinda was already underway by the time cameras rolled on “Boom.” “We’d done a lot of auditions and it wasn’t quite clicking,” Davies explains. “That notion of having her be an equal with the Doctor was very hard to cast.” Then, after watching “Boom” for the 51st time, the showrunner says he kept thinking, “God, I wish I could work with her.”

Suddenly, Davies realized that the answer was right in front of him. “It just clicked. I went, ‘Well, I can. We could just bring her back!'” he recalls. “That was the fastest ‘yes.’ I remember I sent an email, not just to the people I work with, but to the BBC, to Disney+ — absolutely instant answers, saying ‘Yes, yes, yes.’ We all loved her. So it was actually one of the easiest pieces of casting we’ve ever had. Joyous.”

Sethu tells EW that she was ecstatic when she received her invitation back into the Whoniverse. “It was the best feeling ever,” she says. “I couldn’t believe I got to come back. The timing was crazy — I’d finished Andor season 2 and had done ‘Boom,’ and then I went traveling that summer, and that’s when the strikes happened. So when I came back, I just thought, ‘Well, I guess I’m not going to work.'”

That’s when the phone call came. “It just felt totally unbelievable,” she says. “I just didn’t think I’d get a shot at it again, I was completely over the moon. I was so, so happy to be back.”

Belinda’s introduction on the show happens somewhat perplexingly. “One of the puzzles of the series is that the Doctor has been told to go and find Belinda Chandra,” Davies explains. “For once, it’s the Doctor actually chasing after her. Her story has already started, and the Doctor has to run to keep up with her and mysteriously already knows her name.” The showrunner also promises that the mystery delivers major answers about Belinda’s arc halfway through the new season: “It unwraps over the next few episodes. You don’t have to wait for the end of the series for that.”

Despite her frustration with the Doctor, Belinda is still awestruck the first time she enters the TARDIS — and Sethu was similarly overwhelmed the first time she saw the set. “I’m not just saying this: It really took my breath away,” the actress recalls. “It’s so much bigger than you think it’s going to be. It obviously looks massive on screen, but then when you’re actually in it, it’s so expansive. It was such a special moment.”

Davies says that the new batch of episodes aren’t “madly” serialized, but Belinda’s journey home serves as the “spine” for the whole season. “She needs to return home because her next shift starts at 7:30 a.m. on Saturday the 24th of May,” he says. “The whole program was aiming to get there, and yet there’s something wrong with that day. There’s something wrong with that date, and that is all heading towards a monstrous big finale where we find out what’s happening.”

Belinda isn’t the only companion who’ll appear this season. Gibson’s Ruby Sunday, who accompanied Gatwa’s Doctor during his first season before he left her behind with her family, will make a prominent return a few episodes into Belinda’s run. “Ruby’s story is like, what happens to a companion once your life with the Doctor ends?” Davies teases. “What happens to life back on Earth? And believe you, me, that’s going to bring some PTSD with it. You’ve really been through some stuff, but it’s a beautiful chance to stretch and explore Millie’s character and Millie’s performance as well.”

Ruby’s storyline will have a strong romantic component, as the show is introducing Jonah Hauer-King (The Little Mermaid) as Conrad, her love interest. “He’s absolutely delightful and such a part of the team,” Davies says. “It’s a love story about: How do you find a man in your life to replace the Doctor? And for Conrad, it’s: How on Earth do you live up to the Doctor’s ideal? This woman used to keep company with the most exciting man in the universe. How can he be the Doctor in her eyes? And that’s a story that gets very complicated.”

Davies says that Gibson will also return for the season finale. “Lots more Ruby Sunday to come, I promise you,” he says. “She’s back from the moment she left. She never actually left, in fact.”

The showrunner also believes that Gatwa continues to outdo himself with every episode. “I think he grows every day,” Davies says. “When he stepped into those shoes, he got it from day one, so we have to keep working hard to make sure that we push the Doctor. The latest Christmas special showed the Doctor’s loneliness. There’s a great sequence in one of the episodes this year where we see how angry he can get. In the finale, he’s absolutely pushed to the limits like never before, talking about being alone and powerless and defenseless and literally risking everything.”

Gatwa says that his performance evolves with every new adventure — and he feels more at ease in the TARDIS than ever before. “Naturally, you just respond to the material that you are given, and we’re in completely different new worlds this season,” he explains. “The Doctor’s in a different place. I’ve had a full season and I’ve done a couple of specials, so I feel a bit more comfortable with him now. I guess ultimately, he just felt more comfortable in my skin — or I felt more comfortable in his skin, rather.”

Davies gives effusive praise to the show’s lead. “He’s ferocious. He’s a limitless actor,” he says of Gatwa. “He’s a joy. He’s a force in the world. I mean, I think the man is a great force for good and it’s a joy to work for him, to serve him with scripts that will show all those talents under the greatest spotlight, with the most noise and fuss and visibility we can possibly muster. I think we’re doing him proud.”

The new season of Doctor Who premieres on BBC and Disney+ on April 12.