They do it with mirrors

Responding to her friend Carrie's urgent invitation, Miss Marple senses danger when she arrives at her friend's sprawling estate. To Miss Marple's surprise, Carrie's remote Gothic monstrosity has been turned into a rehabilitation center for delinquent boys. Some of Carrie's own children and grandchildren have also taken up residence at Stonygates and have mixed feelings about the way their mother is squandering the family fortune. Then the brutal murder of a stranger to Stonygates would indicate that philanthropy is the least of Carrie's problems. Pure coincidence? Miss Marple thinks not, but must use all her cunning to solve the riddle of the stranger' visit -- and his murder.