"Nothing. At least I hope not--yet. It is what _may_ happen to her that
frightens me so." She took the two threatening letters from her handbag
and gave them to the detective. "These came yesterday," she said,
simply.

Duvall took the letters, and proceeded to read them with the utmost
care. When he looked up, his eyes were sparkling with interest.

"The first letter, I observe," he said, "was mailed night before last,
at half-past six, at the general post office. How was the other letter
delivered?"

"I do not know. I found it, yesterday forenoon, upon the floor in my
daughter's bedroom, an hour or more after she had left the house. She
has not seen it. I kept all news of it from her, as I did not wish her
to be frightened."

"That was wise, of course," Duvall said. "But how could the letter
possibly have been placed where you found it, without your knowledge?
Who, beside yourself, was in the apartment at the time?"

"No one but an old negro cook, who has been with me for years. I am
quite certain that she had nothing to do with it."

"And the maid of whom you speak?"

"She had left my daughter's room, and come into the dining room, where I
was sitting, before Ruth left the bedroom. They went out together. The
note could not have been in the bedroom then, or my daughter would
certainly have seen it. The thing seems almost uncanny."

Duvall began to stroke his chin, a habit with him when he was more than
usually perplexed. Presently he spoke.

"One thing I have learned, Mrs. Morton, after many years spent in
detective work. There is no circumstance, however mystifying it may at
first appear, which is not susceptible of some reasonable and often very
commonplace explanation. You find this letter on the floor in your
daughter's bedroom. It was placed there, either by someone within the
apartment, or by someone from without. Now you tell me that it could not
have been placed from within. Then I can only say that someone must have
entered the room, or at least managed to place the letter in the room,
from outside."

"That may be true, Mr. Duvall," remarked Mrs. Morton, quietly, "but when
you consider that our apartment is on the fourth floor, that one of the
windows of the room was closed, and the other only open a few inches,
and that the blank wall of the opposite house is at least ten feet away,
I fail to see how what you suggest is possible."

Her words filled Duvall with surprise. If what his caller sa