Quite often withDoctor Who, you mash up two genres, says Moffat.

Here, youve got the the magic and madness ofDoctor Whomeets the absolute silliness of superheroes.

I think Stevens managed to invoke an old Christopher ReeveSupermanmovie, says Capaldi.

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Hes sort of made one of those.

Thats what it is.

Its a Christmas special you want to see again and again, I think.

ENTERTAINMENT WEEKLY: The Return of Doctor Mysterio also stars Justin Chatwin fromShameless.

What was it like working with him?

He was absolutely wonderful.

And as soon as the camera starts rolling, theyre absolutely pitch perfect and focused.

I thought he was brilliant.

Is the episode scary?

CAPALDI:Its scarier than Steven thinks it is, I think.

Its something quite out of leftfield that usually frightens them.

So, I dont know.

Its a big, open-hearted adventure.

People keep describing it as very moving, and so Ill go with that.

[Laughs]

Tonally, its quite close to the first of the Christopher ReeveSupermanmovies.

Did you find any crime?

And then I tried to get home, without being seen by my friends, and failed.

I denied who I was.

All my friends recognized me.

Theyd say, Hello, Steve!

And Id say, Im not Steven, Im Red Rat!

So, it was a disaster.

Crime remained rife in Paisley, despite my best attempts at going down those mean streets.

CAPALDI:But they still talk about Red Rat!

Watch the trailer for theDoctor Whospecial Christmas episode below.