This is a wonderful novel. I fell in love with the voice, which reminded me of Dodie Smith's "I Capture the Castle". It's a precocious 15 year old's journal, as she navigates the confusions of adolescence, darkened by her sister's death. She's lost her home with her extended family in Wales, and is living in an English girl's boarding school, with holidays at her father's house -- the father that she just met for the first time. Her world includes fairies, and magic, and Walton does an amazing job of making that both believable, and at the same time making it feasible for it to be all in Mori's imagination. Mori is confident and analytical. She turns that analysis on herself, what she sees around her, and the books she reads. That logical analysis can be quite funny, as she tries to make sense of the scoring system and rules in her new boarding school and family.
She adores books, especially SF and fantasy. This book is a love letter to librarians, to interlibrary loan, and to SF fandom. She mentions all the books she's reading, with wonderful comments on them. It conjures up the wonder of discovering books as a child, if you were one of those kids. While many of the books she mentions are SF or fantasy, not all are. Others that come up include Josephine Tey, Mary Renault, Plato, Shakespeare, and T. S. Eliot. She is thoroughly steeped in SF, though. When she has nightmares, and wakes up terrified, she uses the litany against fear from Dune, and it works.