If I had to describe this episode in just 5 words, it would be… filler but a good one. This review is likely to be short as not much really happened, but it wrapped up last weeks episode in a nice way.
One of the reasons I enjoyed this episode is that it was Clara lite, which gave the Doctor & Williams plenty of time together, which could provide a taste of a future Tardis partnership… Williams and Capaldi seem to have a great chemistry on screen, and they work really well together. The idea of Williams character not having a name and forgetting most of her life was a great twist, and added some real depth.
Most of the episode focused on this which meant that the plot never really got going, and the villain of the episode felt unimportant. There were some laughs, some decent scenes, some forgettable ones, but it was meant to be the Capaldi and Williams show, and it very much was so. One thing I want to mention is next weeks trailer, wow. Zygons, Osgood, Kate, links to the 50th, looks like it should be a cracker.