Bailey took Lizzie under the arms and started to execute the order.  But the sometime colleen from Kerry did not depart without one Parthian arrow.

“Don’t shove,” she said in tones of the greatest dignity as she stumbled into the Hidden Room.  “I’m damn glad to go!”

The iron doors shut behind her.  Bailey watched the Unknown intently.  One moment of relaxed vigilance and—­

But though the Unknown was unlocking the door with his left hand the revolver in his right hand was as steady as a rock.  He seemed to listen for a moment at the crack of the door.

“Not a sound if you value your lives!” he warned again, he shepherded them away from the direction of the window with his revolver.

“In a moment or two,” he said in a hushed, taut voice, “a man will come into this room, either through the door or by that window—­the man who started the fire to draw you out of this house.”

Bailey threw aside all pride in his concern for Dale’s safety.

“For God’s sake, don’t keep these women here!” he pleaded in low, tense tones.

The Unknown seemed to tower above him like a destroying angel.

“Keep them here where we can watch them!” he whispered with fierce impatience.  “Don’t you understand?  There’s a killer loose!”

And so for a moment they stood there, waiting for they knew not what.  So swift had been the transition from joy to deadly terror, and now to suspense, that only Miss Cornelia’s agile brain seemed able to respond.  And at first it did even that very slowly.

“I begin to understand,” she said in a low tone.  “The man who struck you down and tied you in the garage—­the man who killed Dick Fleming and stabbed that poor wretch in the closet—­the man who locked us in downstairs and removed the money from that safe—­the man who started that fire outside—­is—­”

“Sssh!” warned the Unknown imperatively as a sound from the direction of the window seemed to reach his ears.  He ran quickly back to the corridor door and locked it.

“Stand back out of that light!  The ladder!”

Miss Cornelia and Dale shrank back against the mantel.  Bailey took up a post beside the window, the Unknown flattening himself against the wall beside him.  There was a breathless pause.

The top of the extension ladder began to tremble.  A black bulk stood clearly outlined against the diminishing red glow—­the Bat, masked and sinister, on his last foray!

There was no sound as the killer stepped into the room.  He waited for a second that seemed a year—­still no sound.  Then he turned cautiously toward the place where he had left the satchel—­the beam of his flashlight picked it out.

In an instant the Unknown and Bailey were upon him.  There was a short, ferocious struggle in the darkness—­a gasp of laboring lungs—­the thud of fighting bodies clenched in a death grapple.