In her youth, Dee was studying mathematics, though those plans were derailed and now in middle age she serves as the temporary caretaker for the children of professors and administrators at Oxford University. She still spends a lot of her time doing math research, and tells both the reader and others around her what it means to prove a theorem, although she refuses to give even a hint about what she is working on. Mathematics comes up in a few other ways as well. She gives Felicity Penrose Tiles to color, talks about Fibonacci when the child adopts a cat with that name, and often uses mathematical metaphors. Moreover, she initially meets Felicity's father by Oxford's "Mathematical Bridge", and that returns as a key metaphor near the end of the novel.

In some ways, all of the mathematics is entirely tangential to the story. It is Dee's "hobby" and the plot would not necessarily have been different had she been a stamp collector or poet. However, I would argue that the author is actually utilizing mathematician stereotypes. On the one hand, making Dee a mathematician may give the reader the impression that she must be very intelligent. Moreover, being interested in math is considered "quirky" by many people (and most of the characters in this book are quirky in one way or another). Many people also associate mathematicians with mental instability and cold-heartedness. Personally, I think that is both unjust and unjustified, but it serves the author's purposes because she keeps readers on edge, never sure if they trust Dee's narration, never sure if she is completely sane, never sure whether she is ethical.

I am grateful to Karen (whose last name I do not know) for bringing this book to my attention back in July 2020. It only became available in the US in 2021 and I thoroughly enjoyed reading it.