They Do It With Mirrors (Miss Marple, #5)

A sense of danger pervades the rambling Victorian mansion in which Jane Marple's friend Carrie Louise lives—and not only because the building doubles as a rehabilitation centre for criminal youths. One inmate attempts, and fails, to shoot dead the administrator. But simultaneously, in another part of the building, a mysterious visitor is less lucky. Miss Marple must employ all her cunning to solve the riddle of the stranger's visit, and his murder—while protecting her friend from a similarly dreadful fate.