He appeared to be quite disturbed about something, and talked to his companion rapidly and excitedly, but in low tones.

“You were very imprudent to try to dispose of so many at one place,” Mona overheard his companion say, in reply to some observation which he had previously made, and then a great shock went tingling through all her nerves as her glance fell upon the dress which the woman wore.

It was a fine, heavy ladies’ cloth, of a delicate shade of gray—­just the color, Mona was confident, of that tiny piece of goods which Ray had shown her at Hazeldean, and which had been torn from the dress of the woman who had trapped him into Doctor Wesselhoff’s residence, and stolen his diamonds.

She was very much excited for a few moments, and her heart beat with rapid throbs.

Could it be possible that this woman had been concerned in that robbery?

That woman had had red hair, and according to Ray’s description, was much younger; but she might possibly be the other one, who had made arrangements with the physician for Ray’s treatment.  At all events, Mona was impressed that she had found the dress in which the fascinating Mrs. Vanderbeck had figured so conspicuously.

Her face flushed, her fingers tingled with the rapid coursing of her blood, and she felt as if she could hardly wait until the woman should rise, so that she might look for a place that had been mended in the skirt of her dress.

She resolved that she would ride as long as they remained in the car, and when they left it, she would follow them to ascertain their stopping place.

She could not catch anything more that they said, although she strained her ears to do so.

Those few words which she had overheard had also aroused her suspicions—­“you were very imprudent to try to dispose of so many in one place,” the woman had said, and Mona believed she had referred to diamonds; her vivid imagination pictured these people as belonging to the gang of robbers who had been concerned in the Palmer robbery, and now that the excitement attending it had somewhat subsided, they had doubtless come to St. Louis to dispose of their booty; while it was the strangest thing in the world, she thought, that she should have happened to run across them in the way she had.

They were drawing very near the Southern Hotel, where Mona and Mrs. Montague were stopping; but the excited girl resolved that she would not get out—­she would ride hours rather than lose sight of these two strangers, and the chance to ascertain if that gray cloth dress was mended—­“on the back of the skirt, near the right side, among the heavy folds.”  Ray had told her that was where the tear was.

But what if she should find it there?  What should she do about the matter? were questions which arose at this point to trouble her.  What could she, a weak girl, do to cause the arrest of the thieves? how was she to prove them guilty?