ed. 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.

"Probably nothing," Howells answered, "because, as I have said, success
depends upon the courage of a man who kills in the dark while his victim
sleeps. I simply give him the chance to attack me as he did Mr.
Blackburn. Of course he realizes it would be a good deal to his advantage
to have me out of the way. I ask him to come, therefore, as stealthily as
he did last night. I beg him to match his skill with mine. I want him to
play his miracle with the window or one of the locks. But I'll wager he
hasn't the nerve, although I don't see why he should hesitate. He's a
doomed man. I shall make my arrest in the morning. I shall publish all my
evidence."

Bobby wouldn't meet the narrow, menacing eyes, for he knew that Howells
challenged him to a duel of slyness with the whole truth at stake. The
detective's manner increased the hatred which had blazed in Bobby's mind
when he had stood in the bedroom over his grandfather's body. For a
moment he wished with all his heart that he might accept the challenge.
He did the best he could.

"I gather," he said, "that you haven't unearthed the motive for
disturbing the body. And have you found the sharp instrument that
caused death?"

The detective answered tolerantly:

"I have found a number of sharp instruments. None of them, however, seems
quite slender or round enough. I'll get all that out of my man when I
lock him up. I'll get it to-night if he dares come."

"Why," Graham said, "do you announce your plans so a