New Episode tonight on BBC One and BBC America!

Episode Description: A hunt for the lost Ninth Roman Legion leads the Doctor, Bill and Nardole into the middle of an ancient battle that could cast humanity into the dark forever. What is inside the cairn? And how far will they have to go defeat the terrifying alien Eaters of Light?

A long time ago, the ninth legion of the Roman army vanished into the mists of Scotland. Bill has a theory about what happened, and the Doctor has a time machine. But when they arrive in ancient Aberdeenshire, what they find is a far greater threat than any army. In a cairn, on a hillside, is a doorway leading to the end of the world…