Hutchinson Hatch gathered up his overcoat and took the steps coming down two at a time. There was no car in sight, nothing on wheels in fact, until — yes, here was an automobile turning the corner, an automobile cab drifting along apparently without purpose. Hatch hailed it.

“Get me out to Commonwealth Avenue and Arden Street in a hurry!” he instructed. “Take a chance with the speed law, and I’ll make it worth while. It’s important.”

He yanked open the door, stepped in, and closed it with a slam. The chauffeur gave a twist to his lever, turned the car almost within its length, and went scuttling off up street.

Safely inside, Hatch became suddenly aware that he had a fellow passenger. Through the gloom he felt, rather than saw, two inquisitive eyes staring out at him, and there was the faintest odor of violets.

“Hello!” Hatch demanded. “Am I in your way?”

“Not in the slightest,” came the voice of a woman. “Am I in yours?”

“Why — I beg your pardon,” Hatch stammered. “I thought I had the cab alone — didn’t know there was a passenger. Perhaps I’d better get out?”

“No, no!” protested the woman quickly. “Don’t think of it.”

Then from outside came the bellowing voice of a policeman. “Hey, there! I’ll report you!”

Glancing back, Hatch saw him standing in the middle of the street jotting down something in a note book. The chauffeur made a few uncomplimentary remarks about bluecoats in general, swished round a corner, and sped on. With a half smile of appreciation on his lips, Hatch turned back to his unknown companion.

“If you will tell me where you are going,” he suggested, “I’ll have the chauffeur set you down.”

“It’s of no consequence,” replied the woman a little wearily. “I am going no place particularly — just riding about to collect my thoughts.”

A woman unattended, riding about in an automobile at fifteen minutes of eleven o’clock at night to collect her thoughts! And the chauffeur didn’t know he had a passenger! The reporter sat oblivious of the bumping, grinding, of the automobile, trying to consider this unexpected incident calmly.

“You are a reporter?” inquired the woman.

“Yes,” Hatch replied. “How did you guess it?”

“From seeing you rush out of a newspaper office in such a hurry at this time of night,” she replied. “Something important, I dare say?”

“Well, yes,” Hatch agreed. “A jewel robbery at a ball. Don’t know much about it yet. Just got a police bulletin stating that Mrs. Windsor Dillingham had been robbed of a necklace worth thirty thousand dollars at a big affair she is giving tonight.”

The inside of the cab was lighted brilliantly by the electric arc outside, and Hatch had an opportunity of seeing the woman face to face at close range. She was pretty; she was young; and she was well dressed. From her shoulders she was enveloped in some loose cloak of dark material; but it was not drawn together at her throat, and her bare neck gleamed.

There being nothing whatever to say, Hatch sat silently staring out of the window as the automobile whirled into Commonwealth Avenue and slowed up as it approached Arden Street.

“Will you do me one favor, please?” asked the woman.

“Yes, if I can,” was the reporter’s reply.

“Allow me, please, to get out of the automobile on the side away from the curb, and be good enough to attract the attention of the chauffeur to yourself while I am doing it. Here is a bill,” and she pressed something into Hatch’s hand. “You may pay the chauffeur a tip for the passenger he didn’t know he had.”

Hatch agreed in a dazed sort of way, and the automobile came to a stop. He stepped out on the curb, and slammed the door as the chauffeur leaped down from his seat. From the other side came an answering door slam, as if an echo.

Five minutes later Hatch joined Detective Mallory inside. At just that moment the detective was listening to the story of Mrs. Dillingham’s maid.

“There’s nothing missing but the necklace,” she explained; “so far, at least, as we have been able to find out. Mrs. Dillingham began dressing at about halfpast eight o’clock, and I assisted her as usual. I suppose it was halfpast nine when she finished. All that time the necklace was in the jewel box on her dressing table. It was the only article of jewelry in the box.

“Well, the butler came up about halfpast nine o’clock for his final instructions, and Mrs. Dillingham went into the adjoining room to talk to him. It was not more than a minute later when she sent me down to the conservatory for a rose for her hair. She was still talking to him when I returned five minutes later. I put the rose in her hair, and she sent me into her dressing room for her necklace. When I looked into the jewel box, the necklace was gone. I told Mrs. Dillingham. The butler heard me. That’s all I know of it, except that Mrs. Dillingham went into hysterics and fainted, and I telephoned for a doctor.”

Detective Mallory regarded the girl coldly; Hatch knew perfectly what was coming. “You are quite sure,” asked the detective, “that you did not take the necklace with you when you went down to the conservatory, and pass it to a confederate on the outside.”

The sudden pallor of the girl, her abject, cringing fright, answered the question to Hatch’s satisfaction even before she opened her lips with a denial. Hatch himself was about to ask a question, when a footman entered.

“Mrs. Dillingham will see you in her boudoir,” he announced.

From the lips of Mrs. Dillingham they heard identically the same story the maid had told. Mrs. Dillingham did not suspect anyone of her household.

For half an hour the detective interrogated her; then there came a rap at the door, and a woman entered.

“Why, Dora!” exclaimed Mrs. Dillingham

The young woman went straight to her, put her arms about her shoulders protectingly, then turned to glare defiantly at Detective Mallory and Hutchinson Hatch. The reporter gasped — it was the mysterious woman of the automobile. An exclamation was on his lips; but something in her eyes warned him, and he was silent.

When, on the following day, Hutchinson Hatch related the circumstances of the theft of Mrs. Dillingham’s necklace to Professor Augustus S. F. X. Van Dusen — The Thinking Machine — he did not mention the mysterious woman in the automobile. However curious those incidents in which he and she had figured were, they were inconsequential, and there was nothing to connect them in anyway with the problem in hand. The strange woman’s meeting with Mrs. Dillingham in the reporter’s presence had convinced him that she was an intimate friend.

“Just what time was the theft discovered?” inquired The Thinking Machine.

“Within a few minutes of halfpast nine.”

“At what time did most of the guests arrive?”

“Between halfpast nine and ten.”

“Then at halfpast nine,” continued the scientist, “there could not have been many persons there?”

“Perhaps a dozen,” returned the reporter.

“And who were they?”

“Their names, you mean? I don’t know.”

“Well, find out,” directed The Thinking Machine crustily. “If the servants are removed from the case, and there were a dozen other persons in the house, common sense tells us to find out who and what they were. Suppose, Mr. Hatch, you had attended that ball and stolen that necklace; what would have been your natural inclination afterward?”

Hatch stared at him blankly for a minute, then smiled whimsically. “You mean how would I have tried to get away with it?” he asked.

“Yes. When would you have left the place?”

“That’s rather hard to say,” Hatch declared thoughtfully. “But I think I should either have gone before anybody else did, through fear of discovery, or else I should have been one of the last, through excess of caution.”

“Then proceed along those lines,” instructed The Thinking Machine. “You might almost put that down as a law of criminology. It will enable you in the beginning, therefore, to narrow down the dozen or so guests to the first and last who left.”

Deeply pondering this little interjection of psychology into a very material affair, Hatch went his way. In the course of events he saw Mrs. Dillingham, who, out of consideration for her guests, flatly refused to give their names.

Luckily for Hatch, the butler didn’t feel that way about it at all. This was due partly to the fact that Detective Mallory had given him a miserable half-hour, and partly, perhaps, to the fact that the reporter oiled his greedy palm with a bill of two figures.

“To begin with,” said the reporter, “I want to know the names of the first dozen or so persons who arrived here that evening — I mean those who were here when you went up to speak with Mrs. Dillingham.”

“I might find out, sir. Their cards were laid on the salver as they arrived, and that salver, I think, has remained undisturbed. Therefore, the first dozen cards on it would give you the names you want.”

“Now, that’s something like,” commented the reporter enthusiastically. “And do you remember any person who left the house rather early that evening?”

“No, sir,” was the reply. Then suddenly there came a flash of remembrance across the stoical face. “But I remember that one gentleman arrived here twice. It was this way. Mr. Hawes Campbell came in about eleven o’clock, and passed by without handing me a card. Then I remembered that he had been here earlier and that I had his card. But I don’t recall that anyone went out, and I was at the door all evening except when I was up stairs talking to Mrs. Dillingham.”

On a bare chance, Hatch went to find Campbell. Inquiry at his two clubs failed to find him, and finally Hatch called at his home.

At the end of five minutes, perhaps, Hatch caught the swish of skirts in the hallway, then the portieres were thrust aside, and — again he was face to face with the mysterious woman of the automobile.

“My brother isn’t here,” she said calmly, without the slightest sign of recognition. “Can I do anything for you?”

Her brother! Then she was Miss Campbell, and Mrs. Dillingham had called her Dora — Dora Campbell!

“Well — er —” Hatch faltered a little, “it was a personal matter I wanted to see him about.”

“I don’t know when he will return,” Miss Campbell announced.

Hatch stared at her for a moment; he was making up his mind. At last he took the bit in his teeth. “We understand, Miss Campbell,” he said at last slowly and emphatically, “that your brother, Hawes Campbell has some information which might be of value in unraveling the mystery surrounding the theft of Mrs. Dillingham’s necklace.”

Miss Campbell dropped into a chair, and unconsciously Hatch assumed the defensive. “Mrs. Dillingham is very much annoyed, as you must know,” Miss Campbell said, “about the publicity given to this affair; particularly as she is confident that the necklace will be returned within a short time. Her only annoyance, beyond the wide publicity, as I said, is that it has not already been returned.”

“Returned?” gasped Hatch.

Miss Campbell shrugged her shoulders. “She knows,” she continued, “that the necklace is now in safe hands, that there is no danger of its being lost to her; but the situation is such that she cannot demand its return.”

“Mrs. Dillingham knows where the necklace is, then?” he asked.

“Yes,&rdq............