Trapped in her own mind and under attack, can Clara turn the tables on her Zygon double? BBC has released a from this Saturday's episode of Doctor Who: "The Zygon Inversion."
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?
Check out the sneak peek in the video below.
Check out images from the episode in our gallery at the bottom of the page.
Doctor Who airs Saturdays at 9 p.m. ET on BBC America.