After the death of her twin sister, Mori Phelps, having run away from her mad and arguably evil mother in Wales, finds herself sent to live with her estranged father in England. Her father's half-sisters, who support him financially and keep him on a short leash, arrange for Mori to go to their old boarding school, Arlinghurst, where she (of course) belongs not at all; even the fairies, when she does eventually see a few, don't talk to her as the ones in Wales often would. And then she starts to get letters from her mother, containing photos of the twins with Mori carefully burned out of them.
I'm such a big fan of Jo Walton's blogging at Tor.com that I'm a little embarrassed to admit this is the first book of hers that I've read. She says that Among Others began as an attempt to mythologize some real events in her life, and I have to think, given what she has posted about her own reading habits as a young person, that Mori is 15 in 1979 and reading a lot of science fiction because Jo was 15 then and had read all those books. It's a coming of age story about finding what I call my tribe and Mori, after Vonnegut, calls her karass; it's a book about what happens when you prepare yourself to die saving the world, and survive; and most of all it's about how if you love books enough, books will love you back.