Extraordinary episode and easily my favorite episode of the whole season. A wonderfully creepy episode, until it turned out to be a false alarm...only to become a different kind of creeper. I especially love the idea of a conscious universe, one whose motivations weren't inherently malevolent but whose actions unintentionally threatened the lives of The Doctor and her companions (such an existence reminded me of "Flatline," one of Capaldi's best).
I'm less certain about the whole idea of anti-zones and solar (Sole? Soul? Not sure what The Doctor said) tracks, but I liked how the existence of this conscious universe was rooted in The Doctor's childhood stories from her fifth gram (she had seven!), which is a nice callback to previous beings and ideas that existed in The Doctor's childhood only for her/him to encounter them later on in life (I can't think of a specific example but I know this has happened before).
I love that this episode not only featured a blind character, but
she was actually played by a blind actress, Ellie Wallwork. Hanne was a great guest character and I enjoyed her interactions with The Doctor and particularly Ryan. However, I wish she had a bit more to do than just fret in fear about her father, but I did like how she
immediately rejected mirror Trine as her actual mother. She could tell from her heightened senses built around her as a blind girl that this person wasn't her mother and I liked how the episode didn't lean too hard into that aspect.
The "mirror" universe (for a lack of a better word) was a fascinating concept and not just because I often imagined as a kid what it would be like to have a whole universe exist inside of a mirror. I particularly liked how the episode's editor flipped all of the footage in that universe, which was most obviously noticeable with Erik's shirt, but also with Graham's hair parting and The Doctor's earrings and hair parting. I also liked how the universe chose to pick the form of a frog and Grace's voice because they pleased it. I hope we get to see that universe again and not just because The Doctor made a new friend.
Bradley Walsh continued to kill it this season and he gave Graham just the right amount of doubt, longing, and acceptance of Grace's sudden appearance and recognition that she wasn't real despite wanting to believe it was her, even if he didn't believe it was her at first. The level of grief that he continues to experience really touches my heart.
Jodie Whittaker was also in high form this episode, between her joy and wonderment of her childhood stories becoming reality and the idea of a conscious universe existing to making a new friend with that universe. She continues to be a revelation as The Doctor and is driving a hard bargain as one of my favorite Doctors.