Betrayal is one of the themes in The Prime of Miss Jean Brodie by Muriel Spark. Set in Edinburgh during the 1930s, the novel centers on a bold, unusual schoolteacher (Miss Brodie) and a small group of girls she takes under her wing. From about the time they're 10 to when they leave school at 17, they're called the "Brodie set," as if they're part of an exclusive club.
Miss Brodie's mission is ostensibly to give the girls a much broader education than they'd receive through the school's ordinary curriculum. But over time it seems that she's trying to mold them to her own liking or fix them in place with her own labels or judgments. I think that's one of the betrayals in the book – when students begin to seem less like students and more like acolytes, or like attendants in the court of a queen. To what extent can Miss Brodie fix their path in life, given her influence over them?
And how empty is her own life, that she needs such a degree of influence over her students? In what ways has she betrayed herself?
At different points in the book, the narrative flashes forward to show the girls as adults. It's revealed that one of them betrays Miss Brodie to the headmistress of the school by revealing the teacher's fascist sympathies. Miss Brodie's admiration of fascism seems like it's based on puffed-up fantasies (also, it's interesting how the nonconformity of Miss Brodie, who refuses to be like other teachers, co-exists with her fondness for the Blackshirts and with her own desire to mold her students and their paths in life).
When the student informs on her, to what extent is it an act of betrayal? You're left to wonder at all of the motives at play. If Miss Brodie violated the trust and responsibility of her position as teacher, informing on her may be seen as a necessary act, even if her misdeeds have less to do with her misguided admiration of Mussolini and more to do with how she attempts to influence the girls. The student in question may also have been trying to gain some control over Miss Brodie; she may have been struggling with the profound influence Miss Brodie has had on her life. It may be that the student Miss Brodie influences most – the one who becomes most psychologically enmeshed with the errant teacher – is also the one who turns on her.