Everything about this story just *works*

One is characterised brilliantly, the air of 'knowing' that he often has is just done really well, and seeing him at coal hill, before An Unearthly Child could feel off, but I think is just done really well here.

The glimpses we get of other doctors and companions through the framing device are also great, and anything where we get to see more of Sarah Jane is going to be just brilliant. I love the idea of Eleven just popping in from time to time to catch up, leaving a fez for Clyde, it's just really fun.

Shivani is also beautifully done for a one off companion, especially one that's in such a short story. The glimpse we get of her past and the parallels made between her and The Doctor, both being immigrants, are just done so so well.

The ending scene is also great, Twelve coming back to catch up with Shivani is lovely, and then with The Master getting alluded to earlier in the story, the realisation that Missy helped them out, leaving a ladder to make sure they'd survive, it's just done so well and I love it.