“Why did you lock that door?” said Bailey angrily, threatening the Doctor.

“But I didn’t,” said the latter, truthfully enough.  Bailey made a movement of irritation.  Then a glance about the room informed him of the amazing, the incredible fact.  Dale was not there!  She had disappeared!

“You—­you,” he stammered at the Doctor.  “Where’s Miss Ogden?  What have you done with her?”

The Doctor was equally baffled.

“Done with her?” he said indignantly.  “I don’t know what you’re talking about, I haven’t seen her!”

“Then you didn’t lock that door?” Bailey menaced him.

The Doctor’s denial was firm.

“Absolutely not.  I was coming through the window when I heard your voice at the door!”

Bailey’s eyes leaped to the window—­yes—­a ladder was there—­ the Doctor might be speaking the truth after all.  But if so, how and why had Dale disappeared?

The Doctor’s admission of his manner of entrance did not make Lizzie any the happier.

“In at the window—­just like a bat!” she muttered in shaking tones.  She would not have stayed in the doorway if she had not been afraid to move anywhere else.

“I saw lights up here from outside,” continued the Doctor easily.  “And I thought—­”

Miss Cornelia interrupted him.  She had set down her candle and laid the revolver on the top of the clothes hamper and now stood gazing at the mantel-fireplace.

“The mantel’s—­closed!” she said.

The Doctor stared.  So the secret of the Hidden Room was a secret no longer.  He saw ruin gaping before him—­a bottomless abyss.  “Damnation!” he cursed impotently under his breath.

Bailey turned on him savagely.

“Did you shut that mantel?”

“No!”

“I’ll see whether you shut it or not!” Bailey leaped toward the fireplace.  “Dale!  Dale!” he called desperately, leaning against the mantel.  His fingers groped for the knob that worked the mechanism of the hidden entrance.

The Doctor picked up the single lighted candle from the hamper, as if to throw more light on Bailey’s task.  Bailey’s fingers found the knob.  He turned it.  The mantel began to swing out into the room.

As it did so the Doctor deliberately snuffed out the light of the candle he held, leaving the room in abrupt and obliterating darkness.

CHAPTER SEVENTEEN

ANDERSON MAKES AN ARREST

“Doctor, why did you put out that candle?” Miss Cornelia’s voice cut the blackness like a knife.

“I didn’t—­I—­”

“You did—­I saw you do it.”

The brief exchange of accusation and denial took but an instant of time, as the mantel swung wide open.  The next instant there was a rush of feet across the floor, from the fireplace—­the shock of a collision between two bodies—­the sound of a heavy fall.