Among Others is told in the form of a diary written during the school year of 1979-80 by Morweena, a Welsh girl of 15 who's left her home to live with her father and his sisters. Well, not to live with them but to attend a British public school that they're paying for. Mor has left her home because of her mother, who's a witch. Mor and her twin sister were involved in some cosmic battle with their mother. The sister was killed, and Mor was seriously injured. We never know what happened exactly or what fiendish scheme Mor and her sister foiled. It doesn't really matter.
Mor herself has the ability to perform magic, and part of the growing up is to decide how to use that ability. She can also see and converse with fairies. She believes all children can, but since down we forget as up we grow, only a few adults can. (Or maybe none of this is true. Mor's telling the story. We don't get anyone else's point of view.)
Mor is scarily bright. At the boarding school she's an almost complete outsider. What sustains her is her reading of SF. Mor has read widely and remembered everything. She has few role models in life, but she learns a lot about the world from her reading. She loves Roger Zelazny and many others. She's not fond of Philip K. Dick. Her opinions about the books she reads are of course one of the more entertaining aspects of the novel.
Outside the school she finds others who share her interests, and she makes friends. She discovers that there are a lot of others like her and that they even have conventions. You can tell that SF is going to play a big role in her life, but not before she faces up to some hard realities.
Does anything in the book happen the way we're told it does, or is Mor just overly imaginative? Or is Walton the narrator behind the narrator, using magic as a metaphor? It's up to the reader to decide that, so you're on your own.
I know nothing about Jo Walton other than that I've been enjoying her comments on books over at Tor.com for a good while now. She's clearly a person who knows and loves SF and has read just about everything in the field. So that's one connection she has with Morwenna, the narrator of Among Others. As for any others, that's for someone else to point out.
Among Others is beautifully written and totally engaging. One of the best things I've read in a while.