. "I shall call upon you again, later in
the day."

Duvall waited until the door had been closed and locked, and the
doctor's footsteps had died away up the iron staircase. He heard them
for a moment, on the floor of the room above, then all was quiet.

In a moment the detective had stepped to the large box in the corner,
behind which lay, he believed, the discarded opera hat. At a glance, he
saw that it was still there. He was about to stoop and pick it up, when
a sudden fear swept over him. Suppose he was being watched. The doctor
was in the room above. The presence in the room of the beam of light
showed clearly that there must be an opening in the ceiling, into the
laboratory. For all he knew, Hartmann might be observing his every
movement. He stopped in his attempt to pick up the hat, and pretended to
be greatly interested in the box and its contents. After making a
careful examination of the labels upon it, he strolled carelessly back
to the other side of the room, and ate the breakfast which the attendant
had left. He supposed it to be breakfast, although he had no realization
of the time. In a moment he felt for his watch, and found that it was
still in his pocket. When he consulted it, however, he saw at once that
it had run down.

After his meal, he began to feel terribly tired and sleepy. At first he
fought off the feeling, realizing that his only hope of freedom lay in
keeping awake, with all his senses alert. Then he thought of the
nerve-racking hours through which he had just passed; the many more
which were likely to follow, and decided that he must have rest at any
cost. He threw himself upon the floor, his head pillowed upon his arm,
and was soon sleeping the deep sleep which follows utter exhaustion.

CHAPTER XVII

All during the afternoon of the day upon which she had first met her
husband during his confinement at Dr. Hartmann's, Grace Duvall wandered
about the place, looking for him, waiting with growing fears for his
appearance. When evening came, and she had failed to find him, she
became greatly alarmed. In her excitement, she forgot the word she had
agreed to send into Brussels by the boy who drove the delivery wagon,
and was just returning to the house when she heard someone calling to
her from the drive. She turned and saw that it was the bread boy, who
had stopped his cart some little distance from the veranda.

"Mademoiselle," he called, "you have dropped your handkerchief." He