“Yes, so you would say. But the fact remains that there isn’t.”

He took the corner of the carpet in his hand and, turning it over, he showed that it was indeed as he said.

“But the under side is as stained as the upper. It must have left a mark.”

Lestrade chuckled with delight at having puzzled the famous expert.

“Now, I’ll show you the explanation. There is a second stain, but it does not correspond with the other. See for yourself.” As he spoke he turned over another portion of the carpet, and there, sure enough, was a great crimson spill upon the square white facing of the old-fashioned floor. “What do you make of that, Mr. Holmes?”