“I noticed it, Mr. Holmes, but you’ll always find scratches round a keyhole.”

“This is recent, quite recent. See how the brass shines where it is cut. An old scratch would be the same colour as the surface. Look at it through my lens. There’s the varnish, too, like earth on each side of a furrow. Is Mrs. Marker there?”

A sad-faced, elderly woman came into the room.

“Did you dust this bureau yesterday morning?”

“Yes, sir.”

“Did you notice this scratch?”

“No, sir, I did not.”