The Bat - Mary Rinehart Roberts

An elite, rich, and spunky older lady rents a country house for the summer along with her skittish Irish maid and her niece. Some servants sort of come with the property but most soon abandon their new matron due to happenings within this large mansion. A converging plot concerns the homeowner (a banker) who has recently died and whose bank has just coincidentally failed -- the suspicion falls upon a youthful bank clerk who is the heart-throb of the old lady's niece. 

The central plot revolves around a mysterious and effective murder/burglar dubbed by the frustrated police as The Bat and who has been operating in the vicinity of this country home. The subsequent happenings in the house are almost slapstick in nature, in the old lady's efforts in solving the mystery of both the infamous Bat's activities and the bank embezzlement.

This is the novelization of the play 'The Bat' (a play which was adapted by Mary Elizabeth Rinehart and Avery Hopwood from her novel 'The Spiral Staircase') credited to Rinehart and Hopwood, but ghostwritten by Stephen Vincent Benét.