THEY DO IT WITH MIRRORS_PB - AGATHA CHRISTIE

"A man is shot at in a juvenile reform home - but someone else dies... Miss Marple senses danger when she visits a friend living in a Victorian mansion which doubles as a rehabilitiation centre for delinquents. Her fears are confirmed when a youth fires a revolver at the administrator, Lewis Serrocold. Neither is injured. But a mysterious visitor, Mr Gilbrandsen, is less fortunate - shot dead simultaneously in another part of the building. Pure coincidence? Miss Marple thinks not, and vows to discover the real reason for Mr Gilbrandsen's visit."