"Instruct your servants, Mr. Rheinholdt, to lock and bar all the doors of the house," the Professor suggested. "No one must leave it until we have heard your mother's story."

The young man obeyed almost mechanically. There was a general exodus of servants from the room. Some one had brought Mrs. Rheinholdt a gla.s.s of champagne. She sipped it and gradually recovered her voice.

"I had just taken the Professor into the little room my husband used to call the museum," she explained, her voice still shaking with agitation.

"I left him there to examine some specimens of beetles. I thought that I would come back through the conservatory, which is the quickest way. I was about half-way across it when suddenly I heard the switch go behind me and all the electric lights were turned out. I couldn't imagine what had happened. While I hesitated, I saw--I saw--"

She broke down again. There was no doubt about the genuineness of her terror. She seemed somehow to have shrunken into the semblance of a smaller woman. The pupils of her eyes were distended, she was white almost to the lips. When she recommenced her story, her voice was fainter.

"I saw a pair of hands--just hands--no arms--nothing but hands--come out of the darkness! They gripped me by the throat. I suppose it was just for a second. I think--I lost consciousness for a moment, although I was still standing up. The next thing I remember is that I found myself shrieking and running here--and the jewels had gone!"

"You saw no one?" her son asked incredulously. "You heard nothing?"

"I heard no footsteps. I saw no one," Mrs. Rheinholdt repeated.

The Professor turned away.

"If you will allow me," he begged, "I am going to telephone to my friend Mr. Sanford Quest, the criminologist. An affair so unusual as this might attract him. You will excuse me."

The Professor hurried from the room. They brought Mrs. Rheinholdt more champagne and she gradually struggled back to something like her normal self. The dancing had stopped. Every one was standing about in little groups, discussing the affair. The men had trooped towards the conservatory, but the Professor met them on the portals.

[Ill.u.s.tration: "CONFESS THY SINS, MY GOOD MAN."]

[Ill.u.s.tration: THE BLACK BOX IS INTRODUCED INTO THE STORY.]

"I suggest," he said courteously, "that we leave the conservatory exactly as it is until the arrival of Mr. Sanford Quest. It will doubtless aid him in his investigations if nothing is disturbed. All the remaining doors are locked, so that no one can escape if by any chance they should be hiding."

They all agreed without dissent, and there was a general movement towards the buffet to pa.s.s the time until the coming of Mr. Sanford Quest. The Professor met the great criminologist and his a.s.sistant in the hall upon their arrival. He took the former at once by the arm.

"Mr. Quest," he began, "in a sense I must apologise for my peremptory message. I am well aware that an ordinary jewel robbery does not interest you, but in this case the circ.u.mstances are extraordinary. I ventured, therefore, to summon your aid."

Sanford Quest nodded shortly.

"As a rule," he said, "I do not care to take up one affair until I have a clean slate. There's your skeleton still bothering me, Professor. However, where's the lady who was robbed?"

"I will take you to her," the Professor replied. Mrs. Rheinholdt's story, by frequent repet.i.tion, had become a little more coherent, a trifle more circ.u.mstantial, the perfection of simplicity and utterly incomprehensible.

Quest listened to it without remark and finally made his way to the conservatory. He requested Mrs. Rheinholdt to walk with him through the door by which she had entered, and stop at the precise spot where the a.s.sault had been made upon her. There were one or two plants knocked down from the tiers on the right-hand side, and some disturbance in the mould where some large palms were growing. Quest and Lenora together made a close investigation of the spot. Afterwards, Quest walked several times to each of the doors leading into the gardens.

"There are four entrances altogether," he remarked, as he lit a cigar and glanced around the place. "Two lead into the gardens--one is locked and the other isn't--one connects with the back of the house--the one through which you came, Mrs. Rheinholdt, and the other leads into your reception room, into which you pa.s.sed after the a.s.sault. I shall now be glad if you will permit me to examine the gardens outside for a few minutes, alone with my a.s.sistant, if you please."

For almost a quarter of an hour, Quest and Lenora disappeared. They all looked eagerly at the criminologist on his return, but his face was sphinxlike. He turned to Mrs. Rheinholdt, who with her son, the butler, and the Professor were the only occupants of the conservatory.

"It seems to me," he remarked, "that from the back part of the house the quickest way to reach Mayton Avenue would be through this conservatory and out of that door. There is a path leading from just outside straight to a gate in the wall. Does any one that you know of use this means of exit?"

Mrs. Rheinholdt shook her head.

"The servants might occasionally," she remarked doubtfully, "but not on nights when I am receiving."

The butler stepped forward. He was looking a little grave.

"I ought, perhaps, to inform you, madam, and Mr. Quest," he said, "that I did, only a short time ago, suggest to the Professor's servant--the man who brought your mackintosh, sir," he added, turning to the Professor--"that he could, if he chose, make use of this means of leaving the house. Mr. Craig is a personal friend of mine, and a member of a very select little club we have for social purposes."

"Did he follow your suggestion?" Sanford Quest asked.

"Of that I am not aware, sir," the butler replied. "I left Mr. Craig with some refreshment, expecting that he would remain until my return, but a few minutes later I discovered that he had left. I will enquire in the kitchen if anything is known as to his movements."

He hurried off. Quest turned to the Professor.

"Has he been with you long, this man Craig, Professor?" he asked.

The Professor's smile was illuminating, his manner simple but convincing.

"Craig," he a.s.serted, "is the best servant, the most honest mortal who ever breathed. He would go any distance out of his way to avoid harming a fly. I cannot even trust him to procure for me the simplest specimens of insect or animal life. Apart from this, he is a man of some property which he has no idea what to do with. He is, I think I may say, too devoted to me to dream of ever leaving my service."

"You think it would be out of the question, then," Quest asked, "to a.s.sociate him with the crime?"

The Professor's confidence was sublime.

"I could more readily a.s.sociate you, myself, or young Mr. Rheinholdt here with the affair," he declared.

His words carried weight. The little breath of suspicion against the Professor's servant faded away. In a moment or two the butler returned.

"It appears, madam," he announced, "that Mr. Craig left when there was only one person in the kitchen. He said good-night and closed the door behind him. It is impossible to say, therefore, by which exit he left the house, but personally I am convinced that, knowing of the reception here to-night, he would not think of using the conservatory."

"Most unlikely, I should say," the Professor murmured. "Craig is a very shy man. He is at all times at your disposal, Mr. Quest, if you should desire to question him."

Quest nodded absently.

"My a.s.sistant and I," he announced, "would be glad to make a further examination of the conservatory, if you will kindly leave us alone."

They obeyed without demur. Quest took a seat and smoked calmly, with his eyes fixed upon the roof. Lenora went back to her examination of the overturned plants, the mould, and the whole ground within the immediate environs of the a.s.sault. She abandoned the search at last, however, and came back to Quest's side. He threw away his cigar and rose.

"Nothing there?" he asked laconically.

"Not a thing," Lenora admitted.

Quest led the way towards the door.

"Lenora," he decided, "we are up against something big. There's a new hand at work somewhere."

"No theories yet, Mr. Quest?" she asked, smiling.

"Not the ghost of one," he admitted gloomily.

Along the rain-swept causeway of Mayton Avenue, keeping close to the shelter of the houses, his mackintosh turned up to his ears, his hands buried in his pockets, a man walked swiftly along. At every block he hesitated and looked around him. His manner was cautious, almost furtive.

Once the glare of an electric light fell upon his face, a face pallid with fear, almost hopeless with despair. He walked quickly, yet he seemed to have little idea as to his direction. Suddenly he paused. He was pa.s.sing a great building, brilliantly lit. For a moment he thought that it was some place of entertainment. The thought of entering seemed to occur to him.

Then he felt a firm touch upon his arm, a man in uniform spoke to him.