"That's all still in play," Chibnall adds. "We knew what we wanted to do last year. We knew what we'd be doing this year would be entirely different because also, partly, it's about the 13th Doctor's time on the show. [We] wanted to feel like that series was accessible to everybody, whatever episode they dropped in. That was really, really important." One of the early criticisms of the "Whittaker era" was that the series did not feature classic monsters. In her second season as the Doctor, that strategy was flipped on its head and episodes have featured the return of the Master (now played by Sacha Dhawan), a cameo from time agent Jack Harkness (John Barrowman) and a storyline entangling the Time Lords with one of the show's iconic classic monsters, the Cybermen. Gallifrey's finest: the first, fifth, third and second Doctors. Credit:BBC Chibnall says the most challenging thing about dealing with criticism over the lack of classic monsters was knowing that Whittaker's second season would feature them heavily. "You want to create appetite and hunger. Steven [Moffat, the preceding producer] had brilliantly done these kind of great big monster [episodes] in Peter Capaldi's last season [as the Doctor] so it's always about how are you creating different parameters for each series." One of the other key story elements in the season was the introduction of a hitherto unseen previous Doctor, in the form of actress Jo Martin. Though never explicitly stated, it is implied that Martin's Doctor falls before the first on-screen Doctor* and she came complete with a classic Doctor Who-era Tardis console room.

"It was bigger than [just another character] and I don't think Jo would mind me saying but the read-through was really emotional," Whittaker says. "Not in the sense of crying, just in the sense that for the two of us, when we sat next to each other and [they say] your names and who you play. It's an incredible thing to share." Doctor-to-Doctor transitions in the series are not usually so intimate. In the classic Doctor Who series, actor Colin Baker refused to film a regeneration scene to become actor Sylvester McCoy; a double was used instead. And Whittaker did not meet her predecessor Peter Capaldi until months after their crossover episode had aired. You have a vision for what you want to do while you're on the show ... and you see that vision out. Executive producer Matt Strevens "We're not on set at the same time for those regeneration moments," Whittaker says. "Obviously, it's happened before in different ways, but for it to happen for her in this unexpected way for her character, but also to have such a kick-ass character to bat off and it be rug-pulling in a way that isn't neat. It was wonderful to play." Though the Jo Doctor only made a handful of appearances, she was treated, Whittaker adds, like any actor taking on the role permanently. "She's a Doctor and she's got her own costume, everything about the process was the same," she says. "My costume was collaborative, her costume was collaborative. There was less build-up in the sense of it didn't start happening, however, many months before [but] it was still the same respect and process to who you're playing."

One of the most complex dances to be danced in Doctor Who is between the story elements the audience claim they want and the story elements they actually want. In shows with passionate fandoms, which would run the gamut from Doctor Who and Star Trek to Star Wars and even the new reboot of Dracula, audiences can pivot quickly from demands for more and criticisms of too much. "I think it sort of cleaves to the basic principle we have and I've had on the show, but I think we all have, is you have a vision for what you want to do while you're on the show, whether you're the Doctor, whether you're a producer, whether you're a writer, and you see that vision out," says Strevens. "And the conversation around what fans want and what audiences want, all that kind of stuff, you just have to trust yourself as a program," he adds. "You can't really be buffeted by those winds because people will change their minds." Strevens points to a scene late in the season where companion Graham is confessing his fear to the Doctor and she responds by saying only that she is socially awkward. "Some people go, I just wanted her to say it's going to be all right, and you go, yes, you do want that, but you don't necessarily need that," Strevens says. "It's a moment for the Doctor to show she's not human."