The Doctor is teleported to his next destination, by those who orchestrated his being handed over from Mayor Me in the last episode. He is being stalked by a figure from his nightmares. He learns he can stop the creature by confessing a truth he does not wish to tell. We see Clara as a projection in his mind palace, a place in his mind where he tries to figure out how to handle challenges. It seems the construct he finds himself in is an interrogation situation. The Doctor discovers why this place exists and then at the end figures out who is behind it. Let’s just say they have a world of hurt in store for them.
One of the biggest themes this episode examines is the Doctors force of will. Once he decides he is doing something he rarely gives up or in. The places he is willing to go to get the job done are scary. Scary, because one is never sure if he will lose sight of what makes him the Doctor. We know during the Time War he did lose sight of this and that is why he does not refer to himself in that incarnation as the Doctor.
We also see the Doctor in mourning from the events of last episode. He lost someone he held dear. That is another reason that those behind it should worry. A grieving Doctor has rarely been one for reason. The Doctor cares very deeply, even if he does not admit this. He buries his grief into figuring out the situation he finds himself in.
This was a wonderful episode. It really pushes the envelope. It does things that previous stories never thought of. I know I am being vague, but as River Song would say, “No Spoilers.” It is intense, gripping and borders on Gothic Horror. I give this one and A.