“Beetles,” the Professor declared, with some excitement, “occupied precisely two months of my time while abroad.  By all means, Mrs. Rheinholdt!”

“We shall have to go quite to the back of the house,” she explained, as she led him along the darkened passage.

The Professor smiled acquiescently.  His eyes rested for a moment upon her necklace.

“You must really permit me, Mrs. Rheinholdt,” he exclaimed, “to admire your wonderful stones!  I am a judge of diamonds, and those three or four in the centre are, I should imagine, unique.”

She held them out to him.  The Professor laid the end of the necklace gently in the palm of his hand and examined them through a horn-rimmed eyeglass.

“They are wonderful,” he murmured,—­“wonderful!  Why—­”

He turned away a little abruptly.  They had reached the back of the house and a door from the outside had just been opened.  A man had crossed the threshold with a coat over his arm, and was standing now looking at them.

“How extraordinary!” the Professor remarked.  “Is that you, Craig?”

For a moment there was no answer.  The servant was standing in the gloom of an unlit portion of the passage.  His eyes were fixed curiously upon the diamonds which the Professor had just been examining.  He seemed paler, even, than usual.

“Yes, sir!” he replied.  “There is a rain storm, so I ventured to bring your mackintosh.”

“Very thoughtful,” the Professor murmured approvingly.  “I have a weakness,” he went on, turning to his hostess, “for always walking home after an evening like this.  In the daytime I am content to ride.  At night I have the fancy always to walk.”

“We don’t walk half enough.”  Mrs. Rheinholdt sighed, glancing down at her somewhat portly figure.  “Dixon,” she added, turning to the footman who had admitted Craig, “take Professor Ashleigh’s servant into the kitchen and see that he has something before he leaves for home.  Now, Professor, if you will come this way.”

They reached a little room in the far corner of the house.  Mrs. Rheinholdt apologised as she switched on the electric lights.

“It is a queer little place to bring you to,” she said, “but my husband used to spend many hours here, and he would never allow anything to be moved.  You see, the specimens are in these cases.”

The Professor nodded.  His general attitude towards the forthcoming exhibition was merely one of politeness.  As the first case was opened, however, his manner completely changed.  Without taking the slightest further notice of his hostess, he adjusted a pair of horn-rimmed spectacles and commenced to mumble eagerly to himself.  Mrs. Rheinholdt, who did not understand a word, strolled around the apartment, yawned, and finally interrupted a little stream of eulogies, not a word of which she understood, concerning a green beetle with yellow spots.

“I am so glad you are interested, Professor,” she said.  “If you don’t mind, I will rejoin my guests.  You will find a shorter way back if you keep along the passage straight ahead and come through the conservatory.”