“I wish to see a detective,” said Mona, flushing hotly beneath the man’s curious glance.

“The men connected with this office are all out just at this moment, miss.  I am a stranger, and only sitting here for a half-hour or so, just to oblige the officer in charge,” the man courteously replied.

“I am very sorry,” said the young girl, with a sigh, “for I have come upon business which ought to be attended to immediately.”

“I am a detective, miss, although I do not belong here.  I’m an officer from New York; but if you see fit to tell me your business, perhaps I might advise you,” said the officer, kindly, for he saw that she was greatly troubled.

“You are from New York!” Mona exclaimed, eagerly; “then perhaps it will be better for me to tell you, rather than a St. Louis detective; for the robbery happened in New York.”

The detective’s eyes flashed with sudden interest at this.

“Ah!” was all he said, however, and this very quietly.

“Yes, it was a diamond robbery.  A dress worn by one of the persons connected with it was torn; a small piece was entirely cut out of it.  I have found the dress; I have fitted the piece into the rent, and now I want the woman who owns it to be arrested and examined,” Mona explained, in low, excited tones, but very comprehensively.

“Ah!” said the detective again, in the same quiet tone; “you have reference to the Palmer robbery.”

Mona lifted a pair of very astonished eyes to his face.

“Yes,” she responded, breathlessly; “but how did you know?”

“Because I am looking after that case.  I am in St. Louis upon that very business,” replied the man, with a twinkle in his eyes.

“Are you Detective Rider?” questioned the young girl, wonderingly, and trembling with excitement.

Her companion smiled.

“What do you know about Detective Rider?” he inquired.  Then, as she flushed and seemed somewhat embarrassed, he continued:  “And who are you, if you please?”

“I am—­I am acquainted with Raymond Palmer,” Mona answered, evasively; “he has told me about the robbery and—­”

“Ah! yes.  I understand,” interposed the quick-witted officer, as he comprehended the situation.  “But sit down and tell me the whole story as briefly as possible, and I can then judge what will be best to do.”

He moved a chair forward for her, then sat down himself, where he could watch her closely, as she talked, and Mona related all that we already know regarding the two people whom she had seen upon the street-car, together with all that followed in connection with the discovery of the rent in the gray cloth dress, the sending for the fragment that Ray had preserved, and which had fitted so exactly into the tear.

The detective listened with the closest attention, his small, keen eyes alone betraying the intense interest which her recital excited.