“By George!” cried the inspector. “How ever did you see that?”

“Because I looked for it.”

“Wonderful!” said the country doctor. “You are certainly right, sir. Then a third shot has been fired, and therefore a third person must have been present. But who could that have been, and how could he have got away?”

“That is the problem which we are now about to solve,” said Sherlock Holmes. “You remember, Inspector Martin, when the servants said that on leaving their room they were at once conscious of a smell of powder, I remarked that the point was an extremely important one?”

“Yes, sir; but I confess I did not quite follow you.”

“It suggested that at the time of the firing, the window as well as the door of the room had been open. Otherwise the fumes of powder could not have been blown so rapidly through the house. A draught in the room was necessary for that. Both door and window were only open for a very short time, however.”