The story begins at Devil’s Cairn in Scotland, with a girl who wants to listen for music, and a boy who says it is ghosts who may drag her to hell. On a stone cairn nearby, we see the TARDIS carved.
The Doctor, Bill, and Nardole go back to the 2nd century looking for the ninth legion that disappeared, as a result of a debate about who knows more about Roman Britain. The Doctor talks about the Picts and their stone cairns as like churches. When the Doctor finds a body that has been deformed by the total absence of sunligt, Nardole quips, “death by Scotland.” Meanwhile Bill finds deserters who survived the annihilation of the Roman legion, and is attacked by a strange creature whose slime knocks her out.
One of the Scottish children talks about the Romans and offers a critique of empire. The Doctor finds that one of the cairns is indeed a gateway to another world, an interdimensional temporal rift. A creature the locals call “the eater of light” has been fought and held back for generations, but recently got through and destroyed the Roman legion. We learn that the keeper of the gate let the creature through hoping it would destroy the Romans and that they would in turn weaken the beast.
I loved where the Doctor, asked if he is looking for Bill, said he is looking for the most dangerous place, because either Bill is there and he will rescue her, or she isn’t there in which case she is safe already. I also loved how Bill discovered the very “modern” Roman views of sexuality, after she explains that she only likes women.
I’m really sorry to think of the fact that the Peter Capaldi era is drawing towards its end. There is a cycle that fans go through with each new regeneration, and I have seen it in my own case. I was excited about the prospect of an older Doctor, then unimpressed as the early stories tried to make him simply mean and disagreeable, to thinking that some of his speeches, but also the portrayal of the Doctor by Capaldi himself, represent some of the best moments in the history of the show.
Brace yourself for the cycle to begin again…