Among Others is a fantasy novel centered on fifteen-year-old Welsh girl Morwenna. Morwenna is very different from other girls. She is quirky, precocious, rebellious and intelligent. She has a nearly unhealthy love for science fiction novels. Among her many quirks is the ability to communicate with fairies and the ability to cast magical spells.

Morwenna grew up with her twin sister Mor, whom she loved dearly and did everything with, including commune with fairies in old industrial ruins around South Wales. After a flashback to this period, the book properly begins with Morwenna having run away from her mother (who is a powerful witch) to live with the biological father she never knew, Daniel. Morwenna's leg has been crippled, and her twin sister is dead. The exact reasons are not yet specified.

Daniel lives in a grand old estate and is henpecked by his three sisters, whom Morwenna refers to as the three aunts. Morwenna is sent away to boarding school at a place called Arlinghurst. Her rebellious ways and weird qualities make her a loner who is mocked by the rich girls who attend the school, though she does make a couple of friends, including Deirdre.

Morwenna's constant love is reading, particularly science fiction novels, to the point she reads a novel or two a day. Much of the book is filled with Morwenna's commentaries of the merits of particular (real) novels by authors such as Robert Heinlein, J. R. R. Tolkien, C. S. Lewis, and Samuel Delany. In particular, Morwenna loves Tolkien and Lord of the Rings. The themes in the books help Morwenna understand what's going on in her own life.

Important people in Morwenna's life include her Auntie Teg, her grandfather Grampar (who is in a nursing home), and Daniel's father Sam, an elderly Jewish man who connects with Morwenna on an intellectual level.

Morwenna eventually joins a book club at the library after casting a "karass" spell which is supposed to create a magical circle of protection. Morwenna indeed discovers a circle of friends who share her passion. This includes Wim, a nineteen-year-old boy. Morwenna is warned to keep away from Wim because he allegedly got a girl pregnant, but Morwenna is deeply attracted to him. Eventually, Morwenna strikes up a romance with Wim and she reveals that she is a witch. She shows Wim fairies and Wim is able to see them (unlike most people).

In love with Wim and with much to look forward to, Morwenna is able to cast off the shackles of her past, including her grief for her sister and her contentious relationship with her mother. Morwenna rejects the fairies' pleas for her to kill herself in order to become whole again with her sister, choosing life over death. And Morwenna easily defeats her mother in a magical battle. By the end, Morwenna has found love, a new circle of family and friends, and a reason to embrace the future.