In the near future, the Doctor and Clara find themselves on a space shuttle making a suicide mission to the Moon.
Crash-landing on the lunar surface, they find a mining base full of corpses, vicious spider-like creatures poised to attack, and a terrible dilemma.
When Clara turns to the Doctor for help, she gets the shock of her life.
Written by Peter Harness and directed by Paul Wilmshurst the episode guest stars Hermione Norris and Tony Osoba and will air on BBC One on Saturday at 8.30pm.
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