Powers of Darkness by Fred M. White

Alice had very little doubt as to what had happened. Draycott had attempted Moler's life. The mere thought of it set her heart beating painfully fast. She was looking forward anxiously to the time when she should leave this hateful house. It was bad enough to have Moler watching and prying, but the knowledge that Draycott was a cold-blooded assassin came in the nature of a shock. Draycott had deteriorated so rapidly that it might be her turn next.

With a half-smile at her weakness, she shot the bolts of her door. She was too excited to think of sleep. Many singular things about this business puzzled her. Moler must have known whence this attack on his life proceeded; it was impossible to believe that he was ignorant of his assailant. Alice had no doubt, and yet Moler had lied to her when he pretended he was merely suffering from nightmare. All the same, he had been careful to lock the door of his room.