d creature!" she exclaimed, in a horrified tone. Then
wondering if Ray might not have come, while she had been there, she flew
back to the window in the other room to look for him.

Yes, his carriage was standing before the door, and he would soon find
means to release her, she thought.

But moment after moment went by, and no one came, while the continuous
murmur of voices in the room below made her wonder what was going on
there.

Presently, however, her attention was attracted to a man who was
sauntering slowly along the opposite sidewalk, and she was sure she had
seen him somewhere before, although, just at first, she could not place
him.

"Why!" she exclaimed, after studying his face and figure a moment, "it is
Mr. Rider. Can it be possible that he suspects anything of the mystery
concealed in this house? At any rate, he is just the man that is needed
here at this time."

She tapped lightly on the pane to attract his attention.

He stopped, glanced up, and instantly recognized Mona, nodding and
lifting his hat to indicate that he did so.

She beckoned him to cross the street, and then cautiously raised the
window. He was beneath it in a moment.

"Come in, Mr. Rider, and come directly up stairs to me," she said, in a
low tone. "I have been locked in this room, and I have made an important
discovery which you ought to know immediately."

He nodded again, his keen eyes full of fire, turned, ascended the steps,
and pulled the bell.

Mary sighed heavily as she bent her weary steps, for the fifth time, up
the basement stairs to answer his imperative summons.

"Is your mistress at home?" Mr. Rider inquired, in a quick, business-like
tone.

"Yes, sir; but she is engaged with callers," the girl replied.

"So much the better," returned the detective; then, bending a stern look
on her, he continued: "I am an officer; I have business in this house;
you are to let me in and say nothing to any one. Do you understand?"

Mary grew pale at this, and fell back a step or two from the door,
frightened at the term "officer."

Mr. Rider took instant advantage of the situation and stepped within the
hall.

"Don't dare to mention that I am here until I give you leave," he
commanded, authoritatively, and then ran nimbly and quietly up stairs.

It was the work of but a moment to find the room where Mona was confined,
turn the key, and enter.

"What does this mean, Miss Richards?" he asked, regarding her curiously.
"H