That evening, having buttoned his rather shabby old overcoat about him, and taken his crooked walking-stick, Professor Gunn started out for his usual walk.
He strolled along in his accustomed absorbed manner, his head down, buried deep in thought. But it happened that the professor did not walk as far as usual. He had that day been pondering over a most puzzling mathematical problem, and, as he strolled along, carrying his cane behind his back, the solution suddenly dawned on him.
"Hum!" he said, stopping short. "Wonder why I didn’t think of that before?"
Then he felt in his pocket for paper and a pencil. He found the paper, but no pencil. Through every pocket he searched, but not a bit of a pencil could he find.
"Dash it!" he said once more, with greater vehemence. "I must put that down at once, for fear it may slip me."
So he turned and retraced his steps to the academy. Up to his room went the professor.
It had grown dark, and there was no light in his room. Somewhat to his surprise, his key did not seem to work right in the lock, and then, turning the knob, he found the door was not locked at all.
"Carelessness!" he muttered, as he entered the room.
He started to approach the shelf on which the matches were kept. Then, of a sudden, a dark form sprang at him and hurled him against the wall with such violence that he fell to the floor, stunned. The dark figure rushed from the room and vanished.
The professor did not rise for several minutes, When he collected his scattered senses he began to wonder what had happened. His head was ringing, and he felt very weak. With great difficulty he dragged himself to his feet.
His first thought was to raise an alarm. Then he reached for the matches, found them, and struck one. Glancing about, he saw that his desk was in disorder, papers being scattered about and the drawers pulled out.
Then beside the desk he saw something white. He picked it up. It was a handkerchief, with the letters "R. M." on one corner.
"‘R. M.,’" muttered the professor. "Now, whose handkerchief is this? It was dropped by the intruder here. It is a clue to the fellow. ‘R. M.’ Can it be——"
He stopped short, appalled by a thought that came to him.
"The boy was here yesterday," he murmured. "Did he see something here that aroused his cupidity? Is it possible he has entered my room in my absence and——"