n was broken.

The voice had been feminine and had carried a familiar ring. Larry
tried to place it, as he listened at the receiver and attempted to get
the broken connection restored.

"Your party hung up, and won't answer," the operator informed him.

He replaced the receiver on the hook, still seeking to follow the thin
thread of memory given him by the familiar note in that eager excited
voice. If only the girl had spoken a few more words!

* * * * *

Then it came to him.

"Agnes Sterling!" he exclaimed aloud.

Agnes Sterling was a slender, elfish, dark-haired girl--lovely, he had
thought her, on the occasions of their few brief meetings. Larry knew
her as the secretary and laboratory assistant of Dr. Travis Whiting, a
retired college professor known for his work on the structure of the
atom. Larry had called at the home-laboratory of the savant, months
before, to check certain statistics to be used for advertising
purposes and had met the girl there. Only a few times since had he
seen her.

Now she had called him in a voice that fairly trembled with
excitement--and, he thought, dread! And she had been interrupted
before she had time to give him any message.

For a few seconds Larry stared at the telephone. Then he rose abruptly
to his feet, crammed his hat on his head, and started for the door.

"The way to find adventure is to go after it," he murmured. "And this
is the invitation!"

It was not many minutes later that he sprang out of a taxi at the
front of the building in which Dr. Travis Whiting made his home and
maintained a private experimental laboratory. It was a two-story
stucco house, rather out of date, set well back from the sidewalk,
with a scrap of lawn and a few straggling shrubs before it. The door
was closed, the windows curtained blankly. The place seemed deserted
and forbidding.

Larry ran up the uneven brick walk to the door and rang the bell.
Impatiently, he waited a few moments. No sound came from within. He
felt something ominous, fateful, about the silent mystery that seemed
to shroud the old house. For the first time, it occurred to him that
Agnes might be in physical danger, as a result of some incautious
experiment on the part of Dr. Whiting.

* * * * *

Instinctively, his hand sought the door knob. To his surprise, the
door was unlocked. It swung open before him. For a moment he stared,
hesitating, into the d