The two men pushed through the half-open door and stepped out of the foggy London streets and into the brightly-lit entryway of the silent house. There was no indication of a struggle. Everything was neat and in its proper place. They moved silently down the hall, scrutinizing the sitting room, the dining room and the office. Nothing caught the eye of the great detective.

At last they came to the darkened kitchen. Not a sound was heard except a horse and carriage moving past the window at the far end of the room. Light from a gas lamp outside that window poured into a rectangle in the middle of the floor. There it was, perfectly placed in the middle of the yellow box of light: an overturned box of cornstarch. 

"Aha, Watson," said Holmes, "the plot thickens."