A week after we met the Victorians — albeit on Mars — we head back down to Earth and not-so-sunny Scotland where music can be heard coming from some rock formations. Thankfully, Judy, the young girl intent on listening to it, isn’t Outlander-ed through. Instead, we head over to the 2nd century A.D. where Bill and the Doctor are arguing over what happened to the Roman Ninth Legion. She says they’re alive, he insists they’re dead. Nardole is decked out in a bright orange bathrobe that is frankly, quite distracting.
Intent on proving their points, they split up (because that’s always a good idea). Bill goes down to the river to prove there are Romans there, and the Doctor goes looking for a field of dead bodies. Oddly enough, they’re both right.
The Doctor finds most of the already-dead Roman soldiers, but they’re missing all their bones. After a few digs at Scotland, and learning that crows used to speak to humans — it’s not like Stormageddon where only the Doctor could understand the baby, Nardole understands the crow just fine — the pair head over to a nearby cairn (a stone structure kind of like a hut). There they meet a bunch of Picts, or Early Celts (writer Rona Munro, making her return to the series and really making us learn our Scottish history here), who hold them at spear point. They’re waiting for Kar, their leader, and the Guardian of the Gate.
The Doctor manages to distract them with Nardole’s popcorn and beat a hasty getaway. But when he gets to the cairn, he steps into the “door between worlds” (or portal) there and sees what is a watery world, where a dragon-y sea creature (that vaguely resembles the one we saw on Class a few weeks ago) literally comes after him. So he quickly steps back and exits… and discovers that two days have gone by since. Nardole has fully ingratiated himself with the Picts and is now decked out in a blue robe, with those swirly designs on his face. He’s also looked for Bill and failed to find her.
Kar tries to stop them from leaving and the Doctor yells at her, calling her a child who doesn’t quite understand what they’re dealing with. She’s just “making speeches and waving a TV aerial [British for TV antenna] about.” For her part, the young Pict (who can’t be more than a teenager) tells him that in every generation, a slayer warrior is born who went into the gate and fought the Eater of Light (their name for those creatures) and kept it at bay. Only now a creature has gotten through. She’s confident they can defeat it. But the Doctor drops a hell of a reality check on her: there’s more on the other side. Her plan to release it to defeat the advancing Roman legion was a fail because while it destroyed all of them, it still threatens to eat all the sunlight and starlight. Hungry little buggers.
Now the Doctor’s plan is to draw the Beast into the cairn from whence it came and seal it. Something about the morning light opens the portal, so they’ll need to do it then. They’ll also need some of this orange glass-like material that “poisons” the light as the creatures try to feed on it.