My favorite Waters so far, and the first one I think where it consistently crosses the line from fan-fiction+++ over to genuine art. There are some standard Water's elements: an extremely strong sense of place, where the day-to-day tasks and costs of living are constantly reinforced. She would make a great GM, as she is continually mentioning the details of how people work, prepare food, live, travel, etc. etc. It might be ~10% excessive, but still it is a positive and characteristic part of her work. It helps that much of the story is set in London during the Blitz, which while terrible also created a lot of gothic beauty. There's also the standard Water's structural creativity; this time the structure is that there is a social graph, and the story covers a a segment of time for that social graph in 3 different periods. The first part of the story is set in 1947, then the second part in 1944, and then a final segment in 1941. It works surprisingly well, and acts as a sort of in media res that is both initially interesting and also resolves itself into meaningful connections. You can "see" the people and objects in front of you, but you do not know their full history and meaning, and so you are constantly thinking about and unraveling that history until the story arcs start to connect and complete. It also helps that each of the three segments of the book is about half the size of the previous segment, so that story elements resolve steadily more quickly as things go along. A final Water's touch: while the story as a whole is what you might call happy, there are also parts of it that are suuuuuper dark.
Other notes: this is the most modern setting of any of her books that I have read, which I think helped me connect with it. Also, bi-communists! They're coming to steal your women and your men.