He lowered the detective to the floor and straightened up again, listening tensely.  So brief and intense had been the struggle that even now he could hardly believe in its reality.  It seemed impossible, too, that the struggle had not been heard.  Then he realized dully, as a louder roll of thunder smote on his ears, that the elements themselves had played into his hand.  The storm, with its wind and fury, had returned just in time to save him and drown out all sounds of conflict from the rest of the house with its giant clamor.

He bent swiftly over Anderson, listening to his heart.  Good—­the man still breathed; he had enough on his conscience without adding the murder of a detective to the black weight.  Now he pocketed the revolver and the blue-print—­gagged Anderson rapidly with a knotted handkerchief and proceeded to wrap his own muffler around the detective’s head as an additional silencer.  Anderson gave a faint sigh.

The Doctor thought rapidly.  Soon or late the detective would return to consciousness—­with his hands free he could easily tear out the gag.  He looked wildly about the room for a rope, a curtain—­ah, he had it—­the detective’s own handcuffs!  He snapped the cuffs on Anderson’s wrists, then realized that, in his hurry, he had bound the detective’s hands in front of him instead of behind him.  Well—­ it would do for the moment—­he did not need much time to carry out his plans.  He dragged the limp body, its head lolling, into the billiard room where he deposited it on the floor in the corner farthest from the door.

So far, so good—­now to lock the door of the billiard room.  Fortunately, the key was there on the inside of the door.  He quickly transferred it, locked the billiard room door from the outside, and pocketed the key.  For a second he stood by the center table in the living-room, recovering his breath and trying to straighten his rumpled clothing.  Then he crossed cautiously into the alcove and started to pad up the alcove stairs, his face white and strained with excitement and hope.

And it was then that there happened one of the most dramatic events of the night.  One which was to remain, for the next hour or so, as bewildering as the murder and which, had it come a few moments sooner or a few moments later, would have entirely changed the course of events.

It was preceded by a desperate hammering on the door of the terrace.  It halted the Doctor on his way upstairs, drew Beresford on a run into the living-room, and even reached the bedrooms of the women up above.

“My God!  What’s that?” Beresford panted.

The Doctor indicated the door.  It was too late now.  Already he could hear Miss Cornelia’s voice above; it was only a question of a short time until Anderson in the billiard room revived and would try to make his plight known.  And in the brief moment of that resumee of his position the knocking came again.  But feebler, as though the suppliant outside had exhausted his strength.