It was while he was thinking in this way that he felt a startling thing.  It seemed almost as if something touched him.  It made him jump, though the touch was so light and soft that it was scarcely a touch at all, in fact he could not be sure that he had not imagined it.  He stood up and leaned against the wall again.  Perhaps the suddenness of his movement placed him at some angle he had not reached before, or perhaps his eyes had become more completely accustomed to the darkness, for, as he turned his head to listen, he made a discovery:  above the door there was a place where the velvet blackness was not so dense.  There was something like a slit in the wall, though, as it did not open upon daylight but upon the dark passage, it was not light it admitted so much as a lesser shade of darkness.  But even that was better than nothing, and Marco drew another long breath.

“That is only the beginning.  I shall find a way out,” he said.

“I shall.”

He remembered reading a story of a man who, being shut by accident in a safety vault, passed through such terrors before his release that he believed he had spent two days and nights in the place when he had been there only a few hours.

“His thoughts did that.  I must remember.  I will sit down again and begin thinking of all the pictures in the cabinet rooms of the Art History Museum in Vienna.  It will take some time, and then there are the others,” he said.

It was a good plan.  While he could keep his mind upon the game which had helped him to pass so many dull hours, he could think of nothing else, as it required close attention—­and perhaps, as the day went on, his captors would begin to feel that it was not safe to run the risk of doing a thing as desperate as this would be.  They might think better of it before they left the house at least.  In any case, he had learned enough from Loristan to realize that only harm could come from letting one’s mind run wild.

“A mind is either an engine with broken and flying gear, or a giant power under control,” was the thing they knew.

He had walked in imagination through three of the cabinet rooms and was turning mentally into a fourth, when he found himself starting again quite violently.  This time it was not at a touch but at a sound.  Surely it was a sound.  And it was in the cellar with him.  But it was the tiniest possible noise, a ghost of a squeak and a suggestion of a movement.  It came from the opposite side of the cellar, the side where the shelves were.  He looked across in the darkness saw a light which there could be no mistake about.  It was a light, two lights indeed, two round phosphorescent greenish balls.  They were two eyes staring at him.  And then he heard another sound.  Not a squeak this time, but something so homely and comfortable that he actually burst out laughing.  It was a cat purring, a nice warm cat!  And she was curled up on one of the lower shelves