Ruby and Garnet are ten-year-old twins. Identical. They do everything together, especially since their mother died three years earlier. But can being a double act work forever? When so much around them is changing...
The book takes the form of the twins alternately narrating the story of their life in an Accounts book. Ruby and Garnet are ten-year-old identical twins living with their father and grandmother since their mother, Opal, died. The two have always been close despite their differences- Ruby is social, and keen to let her opinions be heard, while introverted Garnet is content to let Ruby dominate their relationship. When their father gets a new girlfriend(Rose) and a new job, their once stable relationship is thrown into turmoil, as the relationship leads to feelings of betrayal from their father to their late mother, and it comes with a big price- leaving their grandmother behind for a house in the country.
As Ruby is very dominating, she insists that the girls shouldn't stand for their new lifestyle. She and Garnet start off well in school, but once Garnet makes a new friend, Ruby sulks and Garnet quickly changes to stop her feeling upset. After this, they do not behave properly in school and do not talk to anyone else.
The twins find an article about auditions for a TV adaptation of The Twins at St. Clare's, and Ruby is keen to go ahead and audition, even though Garnet and their father do not agree. Surprisingly, Rose is supportive, although her efforts are for nothing, as Garnet and Ruby have to run away to London to audition. Although Garnet isn't keen on the idea, she is about to deliver a good audition but the twins father appears just as she is about to begin, making her feel terrible for messing up the audition.
Near summer, Ruby, realizing that the school where the TV movie is being filmed at is a prestigious boarding school for girls, Marnock Heights, decides that the pair ought to sign up for scholarships- of which there is only one. Despite their father's early hesitation to the idea, he encourages Garnet to go ahead with the school after it is revealed that she won the scholarship. (Ruby was confident that she would win it if they both couldn't 'wangle one' together). Garnet is torn between pleasing her sister and doing something different, for once. Meanwhile, Ruby refuses to talk to her, and often wanders off on her own. She is determined to be different from Garnet, and ends up cutting off her hair.
She does not let herself be around Garnet for the whole summer, and even though they both feel as though they are missing something, Ruby is too proud to apologize while Garnet wishes she was able to. At this point in the novel, Garnet is no longer narrating- Ruby has changed the "book" to a Memorandum, which she continues writing in until the end of the book. After making friends with someone she previously considered rather a bully, Ruby starts to realize that she and Garnet don't need to be the same, and don't have to do the same things, to be happy. She also realizes, alternately, that being together would have helped Garnet feel better about leaving. Ruby finds a friend in Rose, also, who encourages her to say sorry to Garnet.
In the end, Ruby apologizes to Garnet, and they both realize that they can still be together while apart, as long as they remember each other. Garnet leaves for school, and writes a letter about how much she is enjoying it.
Jeremy Tredgold or Blob