Series: 10

Original Air date:  June 17, 2017

Number Doctor: 12th

Companion(s): Bill Potts and Nardole

Writer(s):   Rona Munro

Director(s):  Charles Palmer

Guest Stars:
Michelle Gomez as Missy
Rebecca Benson as Kar
Daniel Kerr as Ban
Brian Vernel as Lucius
Rohan Nedd as Simon
Ben Hunter as Thracius
Sam Adewunmi as Vitus
Billy Matthews as Cornelius
Aaron Phagura as Marcus
Jocelyn Brassington as Judy

Synopsis: A long time ago, the Roman legion of the ninth vanished into the mists of Scotland. Bill has a theory about what happened, and the Doctor has a time machine. But when they arrive in ancient Aberdeenshire, what they find is a far greater threat than any army. In a cairn, on a hillside, is a doorway leading to the end of the world.

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