She heard him mutter something and quickly turn the key in the lock.

Then he seemed to run toward the window, and for some reason to recoil from it.
The next instant she realized that he was coming toward the mantel-room, that he intended to hide in it.

There was no doubt in her mind as to his identity.

It was the Bat, and in a moment more he would be shut in there with her.
She tried to scream and could not, and the next instant, when the Bat leaped into concealment beside her, she was in a dead faint on the floor.
Bailey meanwhile had crawled out on the roof and was carefully searching it.

But other things were happening also.