For Lizzie announced that the Unknown was ranging the second floor hall.  From the time they had escaped from the living-room this man had not been seen or thought of, but that he was a part of the mystery there could be no doubt.  It flashed over Miss Cornelia that, although he could not possibly have locked them in, in the darkness that followed he could easily have fastened the bat to the door.  For the first time it occurred to her that the archcriminal might not be working alone, and that the entrance of the Unknown might have been a carefully devised ruse to draw them all together and hold them there.

Nor was Beresford’s arrival with the statement that the Unknown was moving through the house below particularly comforting.

“He may be dazed, or he may not,” he said.  “Personally, this is not a time to trust anybody.”

Beresford knew nothing of what had just occurred, and now seeing Bailey he favored him with an ugly glance.

“In the absence of Anderson, Bailey,” he added, “I don’t propose to trust you too far.  I’m making it my business from now on to see that you don’t try to get away.  Get that?”

But Bailey heard him without particular resentment.

“All right,” he said.  “But I’ll tell you this.  Anderson is here and has arrested the Doctor.  Keep your eye on me, if you think it’s your duty, but don’t talk to me as if I were a criminal.  You don’t know that yet.”

“The Doctor!” Beresford gasped.

But Miss Cornelia’s keen ears had heard a sound outside and her eyes were focused on the door.

“That doorknob is moving,” she said in a hushed voice.

Beresford moved to the door and jerked it violently open.

The butler, Billy, almost pitched into the room.

CHAPTER EIGHTEEN

THE BAT STILL FLIES

He stepped back in the doorway, looked out, then turned to them again.

“I come in, please?” he said pathetically, his hands quivering.  “I not like to stay in dark.”

Miss Cornelia took pity on him.

“Come in, Billy, of course.  What is it?  Anything the matter?”

Billy glanced about nervously.

“Man with sore head.”

“What about him?”

“Act very strange.”  Again Billy’s slim hands trembled.

Beresford broke in.  “The man who fell into the room downstairs?”

Billy nodded.

“Yes.  On second floor, walking around.”

Beresford smiled, a bit smugly.

“I told you!” he said to Miss Cornelia.  “I didn’t think he was as dazed as he pretended to be.”

Miss Cornelia, too, had been pondering the problem of the Unknown.  She reached a swift decision.  If he were what he pretended to be—­ a dazed wanderer, he could do them no harm.  If he were not—­a little strategy properly employed might unravel the whole mystery.