** spoiler alert ** 
 I saw the movie several months ago and think I like the movie better than the book. The movie seemed to make a better case for the "betrayal" and also for Miss Brodie's "offenses" that led to her, well, no longer being in her prime. 
 **SPOILERS** 
 This story follows a group of girls from about 10 years of age through 18 in the 1930s, with glimpses into their futures. They are processing the impact of an unusual teacher, Jean Brodie. The influence of teachers is interesting, as students may be encouraged or discouraged based on the feedback they receive at an early age. 
 On one hand Miss Brodie is smart and wants her girls to experience culture and worldly matters not covered by the curriculum - the kind of fun teacher we all want. On the other hand, she has an agenda to push and uses the girls to see her views pushed forward - the kind of teacher parents probably fear. From the girls' perspectives, they alternately view her as fabulous/all-knowing and ridiculous/agenda-driven. Sandy, as the main focus of the story, tends to see the latter more than the other girls - and as time goes on would add dangerous to that list. 
 The six "Brodie set" girls seem to represent certain traits - one is smart, another pretty/sex-focused, another into sports, etc. Although this is not my favorite set-up, it works in favor of Miss Brodie steering them into certain directions in this short novel. Like most groups of friends, there are pairings of girls who share certain confidences. In this case, Sandy (smart - going into psychology) and Jenny (pretty - going to be a model or actress) - particularly focus on Miss Brodie's love life, as she is in love with the married art teacher and having an affair with the unmarried music teacher. 
 In the book, I found Sandy's duplicity in both continuing a relationship with Miss Brodie while turning against her to be rather undefined. She was always skeptical about Miss Brodie's views (on sex, on life, and, later, on politics, etc.) but at some point, apparently enough was enough and she mentioned Miss Brodie's fascination with fascism (in the form of Mussolini mostly but also of Hitler) to the headmistress as a means of getting her fired. The trigger was a young girl following her brother to the Spanish Civil War because of Miss Brodie's romanticized view of the War and Franco. 
 In the movie, this was a little more explicit - the girl killed was one of the Brodie set and Miss Brodie's political leanings were a bigger part of the story, as was Sandy's chafing at Miss Brodie's pronouncements about their futures. It seemed more reasonable than in the book. 
 Maybe I just missed something in the book, as I was easily distracted. I enjoyed it and give it a 3.5/5, but it just didn't engage me as I thought it would.