The Mark of the Hand — Charlotte Armstrong

When Betty Follett took a position in the Kilburn household, she thought she had found Paradise---until she learned that murder lurked in someone's heart......The spry old lady who read murder mysteries? The handsome widower who could always be found at the shooting range? The guest who came out of the past with nothing and desired to enter the future with everything?.......Whose was the hand that left the mark of murder?"