The Hand in the Dark by Arthur J. Rees — Read

On his way to Chidelham, Caldew again pondered over the murder, and for the first time seriously asked himself whether Miss Heredith could have committed the crime. He had glanced at that possibility before, and had practically dismissed it on the score of lack of motive, but his sister's story of the differences between Miss Heredith and her nephew's wife supplied that deficiency in a startling degree. In reviewing the whole of the circumstances by the light of the information his sister had given him, it now seemed to him that Miss Heredith fitted into the crime in a remarkable way.

The most important fact leading to that inference was that she alone, of all the inmates of the moat-house the previous night, was out of the dining-room when the murder was committed. That supposition took no cognizance of the servants, but Caldew had all along eliminated the servants in his consideration of the crime. In the next place, it supplied an explanation for the disappearance of the bar brooch from the bedroom. In all likelihood the butler had first acquainted his mistress with his discovery of the unlocked staircase door, and she, realizing where she had dropped her brooch, had seized upon the opportunity to request Musard to call the detective downstairs and tell him about the door. In his absence she returned to the bedroom for the brooch.