And so, here we go again – it’s all change for the Time Lord. Doctor Who invented the sci-fi reboot back in 1966 when the first Doctor William Hartnell’s health began to suffer. But rarely has the show faced such a combination of changes – with Peter Capaldi, showrunner Steven Moffat and Michelle Gomez, who plays Missy (the female version of the Master), all signing off this year.

The first symptom of the changes is John Simm’s return as the earlier Master in this season’s penultimate episode, World Enough and Time. He told Moffat he’d love to return as long ago as his final appearance in 2010’s The End of Time, when David Tennant left. “It’s a role no father can turn down,” Simm explained.

His arrival this week begins an extended finale that will take us as far as a Christmas special, Capaldi and Moffat’s swansong. With the end in sight for Gomez, Capaldi and Moffat, we asked them about Doctors past, present and future...

Peter Capaldi

Why make this your final series? 

I love this show, but I’ve never done anything where you turn up every day for ten months. I want to always be giving it my best and I don’t think if I stayed on I’d be able to do that. I can’t think of another way to say, “This could be the end of civilisation as we know it.”

With episodic television of any genre, the audience wants the same thing all the time – but the instinct that leads the actor is not about being in a groove.

What’s the Doctor Who audience like?

The conventions are a big carnival with a lot of really smart people having a laugh dressing up. The show is quite a benign friend so you get a happy response – people shouting from their cars, “Doctor Who, where’s your Tardis? What are you walking for?”

It still amazes me how huge the show is. I was recently in Minneapolis – where Prince is from. I was recognised so many times by so many people, I couldn’t quite believe it – not because of the character, who I know is world-famous, but because it was me.

What’s the hardest part of being the Doctor?

Doctor Who is a hugely challenging show to write and to act in. It has to turn on a dime from comedy to terror to tragedy. It’s a children’s show that developed into something more complex, a bit more adult-orientated, but we have a duty to play to the seven-year-old as well as the 42-year-old. Sometimes you have to be more comic than you’d normally be comfortable with, but it’s important. 

How would you describe your Doctor?

The Doctor is deeply sad – I think he always has been. When you’re wise and you’ve lived a very long time, that’s how you’d be. Although you have to be careful with very human emotions and the Doctor because he’s an alien. It’s more straightforward to play the human elements, but then it might as well be a cop show.

What’s it like working with Michelle Gomez?

She has such range and energy – and she’s very beautiful. 

She points out that she, you and Steven Moffat are all from Glasgow…

Well, Steven isn’t technically from Glasgow – he’s from Paisley. But he has a Glasgow sense of humour. He always finds what’s funny about you physically and puts it in the script. You suddenly read this description of yourself that is accurate but not always flattering. His presence is more pervasive than most people think.

Scripts come in that need a little work. He goes through them and sorts that out. This season people have compared scripts with his name and without his name and say the others are better. But they’ve all got his touch. 

What can you say about your regeneration?

I can’t go into the details. I know what happens, but I don’t know how it happens. Certainly it’s not straightforward. It’s more complicated than recent ones. That’s one of the appeals of being in the show – it has death at the heart of it. He’s the only hero on TV who dies again and again.