“I meant no harm, sir, I’m sure.  The young woman came to the door last evening—­mistook the house, she did.  And then we got talking.  It’s lonesome, when you’re on duty here all day.”

“Well, what happened then?”

“She wanted to see where the crime was done—­had read about it in the papers, she said.  She was a very respectable, well-spoken young woman, sir, and I saw no harm in letting her have a peep.  When she saw that mark on the carpet, down she dropped on the floor, and lay as if she were dead.  I ran to the back and got some water, but I could not bring her to.  Then I went round the corner to the Ivy Plant for some brandy, and by the time I had brought it back the young woman had recovered and was off—­ashamed of herself, I daresay, and dared not face me.”

“How about moving that drugget?”

“Well, sir, it was a bit rumpled, certainly, when I came back.  You see, she fell on it and it lies on a polished floor with nothing to keep it in place.  I straightened it out afterwards.”

“It’s a lesson to you that you can’t deceive me, Constable MacPherson,” said Lestrade, with dignity.  “No doubt you thought that your breach of duty could never be discovered, and yet a mere glance at that drugget was enough to convince me that someone had been admitted to the room.  It’s lucky for you, my man, that nothing is missing, or you would find yourself in Queer Street.  I’m sorry to have called you down over such a petty business, Mr. Holmes, but I thought the point of the second stain not corresponding with the first would interest you.”

“Certainly, it was most interesting.  Has this woman only been here once, constable?”

“Yes, sir, only once.”

“Who was she?”

“Don’t know the name, sir.  Was answering an advertisement about typewriting and came to the wrong number—­very pleasant, genteel young woman, sir.”

“Tall?  Handsome?”

“Yes, sir, she was a well-grown young woman.  I suppose you might say she was handsome.  Perhaps some would say she was very handsome.  ’Oh, officer, do let me have a peep!’ says she.  She had pretty, coaxing ways, as you might say, and I thought there was no harm in letting her just put her head through the door.”

“How was she dressed?”

“Quiet, sir—­a long mantle down to her feet.”

“What time was it?”

“It was just growing dusk at the time.  They were lighting the lamps as I came back with the brandy.”

“Very good,” said Holmes.  “Come, Watson, I think that we have more important work elsewhere.”

As we left the house Lestrade remained in the front room, while the repentant constable opened the door to let us out.  Holmes turned on the step and held up something in his hand.  The constable stared intently.