Parts: 1 (45-minute)
Writer: Mark Gatiss
Airdate: 10 June 2017
Production Code: n/a

Doctor: twelfth
Companions: Bill, Nardole

Megalomaniac of the Week: Missy
Creature Feature: Ice Warriors

Story: On a day out to NASA headquarters, the Doctor, Bill and Nardole are privy to a top-secret transmission from Valkyrie, which is scanning the surface beneath the Martian poles. What NASA does not expect to find: a message, spelled out in Martian boulders, that reads "GOD SAVE THE QUEEN".

Naturally, the Doctor is curious to investigate the message's origins, which the TARDIS has traced to 1811. Shortly after arriving in the tunnels underneath the north pole of Mars, three things happen in rapid succession: the TARDIS whisks Nardole back to Earth, Bill encounters a British soldier wearing a Victorian-era spacesuit, and the Doctor comes face-to-face with the last living Ice Warrior...