The Valley of Silent Men by James Oliver Curwood

Kent did not move. His senses for a space were stunned. He was almost physically insensible to all emotions but that one of shock and horror. He was staring at Kedsty's gray-white, twisted face when he heard Marette's door close. A cry came from his lips, but he did not hear it -- was unconscious that he had made a sound. His body shook with a sudden tremor. He could not disbelieve, for the evidence was there. From behind, as he had sat in his chair Marette Radisson had struck the Inspector of Police with some blunt object. The blow had stunned him. And after that --

He drew a hand across his eyes, as if to clear his vision. What he had seen was impossible. The evidence was impossible. Assaulted, in deadly peril, defending either honor or love, Marette Radisson was of the blood to kill. But to creep up behind her victim -- it was inconceivable! Yet there had been no struggle. Even the automatic on the floor gave no evidence of that. Kent picked it up. He looked at it closely, and again the unconscious cry of despair came in a half groan from his lips. For on the butt of the Colt was a stain of blood and a few gray hairs. Kedsty had been stunned by a blow from his own gun!