Executive producer Chris Chibnall teases a ‘seismic’ episode.

Were not just going big on the finale in episode 10,Doctor Whoexecutive producerChris Chibnalltells EW.

Episode 9, Ascension of the Cybermen, obviously sees the return of iconic monsters.

Doctor Who

Credit: Ben Blackall/BBC Studios/BBC America

Its the first time Jodies Doctor, the Thirteenth Doctor, has squared off against them.

We have both old and new designs of the Cybermen, theres more than one Cyber-variant in the story.

And its a big, space-spanning, spaceship-lasery, Cybermanny sci-fi story.

Doctor Who

Ben Blackall/BBC Studios/BBC America

Enter the Doctor and her friends.

Ascension of the Cybermen guest-stars British actress Julie Graham, who plays a character called Ravio.

You might know her fromThe Bletchley Circleand also a show calledShetland, says Chibnall.

Shes one of the U.K.s most-loved actors.

She plays one of the human refugees.

Chibnall is more tight-lipped about The Timeless Children.

Weve been playing out this mystery for a while now, he says.

The Timeless Children plural!

will pay off a lot of the strands that weve set running both last year and this year.

How does Chibnall think fans will be left feeling once the episode is over?

It is an emotional and narrative roller coaster for the characters, for the audience, he says.

I think youre going to need a very strong drink.

Its a 65-minute finale, so on BBC America that will go longer, obviously.

People, I think, are going to feel wrung-out and possibly a little bit open-mouthed.