“You fell in the doorway so that Miss Mount couldn’t get past,” Bernard resumed. “As she ran into the hall, you wound up the broken thread and stowed it in your pocket while she was looking for the murderer.
“Stimson came and took you upstairs. You were sure that Susan would keep Miss Mount busy as before. So you dismissed everybody on a plea of nervousness and nausea, nipped across the hall, unlocked Miss Mount’s door, restored the key to the inside, replaced the cross-bow and the gloves in Joel’s den, planted your thread in her sewing-drawer and your rope in her clothes-closet and went cheerfully back to bed. Later, you were careful to tell us that you heard a noise outside the library windows before you were shot. If we traced the method and found the nail-hole, the rope and the thread, that would pin the murder and the attempted murder on Miss Mount almost past a doubt!”
Graham turned upon Landis eyes that strove to hide stark terror beneath their indignation.
“Do you believe it?” he demanded hoarsely. “Is it probable?”
“Of course it isn’t!” Bernard cut it. “It’s too clever for that. But those finger-prints will hang you!”
“This—this business just now!” shouted Graham suddenly. “Why should I try to kill you?”
“I haven’t said you did!” was the swift retort. “But you came mighty near it! Only, I was expecting you to try, so I dropped flat as I lowered the window and pulled the thread. Now for your motive! I handed you a sheet of paper a little while ago with a lot of indefinite nonsense on it. You suspected I did it to get your finger-prints. You were right. But I wanted you to know that I suspected you. When you warned us—warned Landis in advance—that our experiment was dangerous, I knew that you had fallen into my little trap!
“A clever trap wouldn’t have caught you, Graham. This was so simple and obvious that you fell for it and tried to kill me. I made a point of telling you that everyone would be downstairs, including the policeman we posted to guard you. That left you a clear road to the cross-bow. One little twitch and it would shoot me instead of shooting through the reception-room doorway!”
“What good would that do?” Graham demanded shrilly. “Landis would remain!”