Afterward he arranged a small card table by the fire in the hall. He found cards, and, with a package of cigarettes and a box of matches convenient to his hand, commenced to play solitaire. The detective, Bobby gathered, had brought his report up to date, for he lounged near by, watching the Panamanian's slender fingers as they handled the cards deftly. Bobby, Graham, and Katherine were glad to withdraw beyond the range of those narrow, searching eyes. They entered the library and closed the door. Graham, expectant of a report from his man in New York as to the movements of Maria and the identity of the stranger, was restless. "If we could only get one fact," he said, "one reasonable clue that didn't involve Bobby! I've never felt so at sea. I wonder if, in spite of Howells's evidence, we're not all a little afraid since this afternoon, of something such as Katherine felt last night--something we can't define. Howells alone is satisfied. We must believe in the hand of another man. Doctor Groom talks about indefinable hands." "Uncle Silas was so afraid last night!" Katherine whispered. "That," Bobby cried, "is the fact we must have." He paused. "What's that?" he asked sharply. They sat for some time, listening to the sound of wheels on the gravel, to the banging of the front door, and, later, to the pacing of men in the room of death overhead. They tried again to thread the mazes of this problem whose only conceivable exit led to Bobby's guilt. The movements upstairs persisted. At last they became measured and dragging, like the footsteps of men who carried some heavy burden. They looked at each other then. Katherine hid her eyes. "It's like a tomb here," Bobby said. He arranged kindling in the fireplace and touched a match to it. It hadn't occurred to him to ring for Jenkins. None of them wished to be disturbed. Eventually it was the detective who intruded. He strolled in, glanced at them curiously for a moment, then walked to the door of the enclosed staircase. He grasped the knob. "To-night," he announced, "I am trying a small experiment on the chance of clearing up the last details of the mystery. Since it depends on the courage of whoever murdered Mr. Blackburn I've small hope of its success." He indicated the ceiling. "You've heard, I daresay, what's been going on up there. Mr. Blackburn's body has been removed to his own room. The room where he was killed is empty. I mean to go up and enter and lock the doors as he did last night. I shall leave the window up as it was last night. I shall blow out the candle as he did." He lowered his voice. He looked directly at Bobby. His words carried a definite challenge. "I shall lie on the bed and await the murderer under the precise conditions Mr. Blackburn did." "What do you expect to gain by that?" Graham asked.