my eye
on you, just the same." He leaned against the door jamb and watched
Duvall as he ascended the stairs.

The detective reached the fourth floor at top speed. He was panting,
when he arrived opposite the door of the apartment he sought. Once
there, he paused for a moment, listening intently. Not a sound came from
the interior of the flat.

The problem of obtaining access to the place now confronted him. The
door was of oak of stout construction. He doubted his ability to break
it in, nor did he wish to attempt to do so, if it could be avoided.
Breaking into private apartments, without a warrant, was a serious
matter. There was a chance that this might not be the right place, after
all. He hesitated. Yet Grace might be within, in danger, perhaps, of her
life. It was imperative that he should find out the truth at once.

Stepping up to the door, he knocked sharply upon it, then waited for a
reply. He scarcely expected one, but felt that he should at least give
the persons within a chance.

A long silence ensued. Duvall was about to rap again, when, to his
amazement, the door slowly and noiselessly swung inward, as though
impelled by some unseen hand.

The room beyond was shrouded in darkness. Duvall could see no one.
Whoever had opened the door must now be concealed behind it. No one
either greeted or challenged him. The door swung three-quarters open,
and stood still. Not a sound was to be heard. The room was as silent as
a tomb.

Duvall stood on the threshold for a few seconds, listening intently. He
was greatly astonished by what had occurred. Why had the door been so
silently opened? Was someone waiting within, ready to attack him the
moment he made a step forward?

Whether this was the case or not, nothing, he reflected, was to be
gained by remaining where he was. Drawing an automatic pistol from his
pocket, he held it in readiness in his right hand, then, raising his
left arm, he flung his entire weight against the partly opened door.

The door yielded to his attack. Then there came a dull thud, as though
some heavy body had fallen to the floor, and immediately after the
hallway resounded with a series of unearthly screams. Duvall still moved
forward. Then, to his utter surprise, there appeared in the darkness a
grotesque figure, which immediately hurled itself upon him and began to
clutch frantically at his throat.

CHAPTER XVIII

It would be difficult to describe the feelings of Grace Duv