The BBC have revealed the official synopsis for The Zygon Inversion, the eighth episode of series 9.
Shapeshifting Zygons are everywhere in the UK, and there is no way of knowing who to trust. With UNIT neutralised, only the Doctor stands in their way. But how do you stop a war? And what can the Doctor do to save his friends?
The episode premiers on BBC1 on 7th November but the time of broadcast is yet to be confirmed.