"The Zygon Invasion" is the seventh episode of the ninth series of the British science fiction television series Doctor Who. It was first broadcast on BBC One on 31 October 2015, and written by Peter Harness and directed by Daniel Nettheim. The episode is the first episode of a two-part story, the second part being "The Zygon Inversion", which aired on 7 November. In the episode, a peace treaty agreed between humans and shapeshifting aliens called Zygons in the 2013 episode "The Day of the Doctor" has started to fail. A radicalised splinter group of Zygons, seeking to no longer hide among humans but be themselves, takes over Zygon High Command, and seeks to invade present-day Earth and neutralise military organisation UNIT. The alien time traveller the Twelfth Doctor attempts to keep the peace.