Miss Pym Disposes by Josephine Tey

A mystery written in 1946, set at a Physical Education school for girls. The crime does not happen until the last third of the book, so you get to know the characters well, especially Miss Pym, who is the narrator of the book, and a guest lecturer in psychology at the school. Tey has little patience for artificiality and I really enjoyed her " asides" as the novel went on.