re opened in the paneled oak
wall a rectangular door, a door of large enough size to admit a man.
From the recess beyond there came a breath of air, foul with the
musty odor of decayed vegetation, dank as the air of a tomb.

"Ah-h-h!" breathed Frank. "So that is where Ed Leland is hiding! The
secret retreat of the gloomy scientist!"

He spoke half jestingly, yet when he squeezed his stalwart bulk
through the opening and flashed the beam of his light into the
darkness of a narrow passage ahead he was assailed with vague
forebodings. Tommy followed close behind and spoke not a word.

* * * * *

The passage floor was thick with dust, but the marks of many footsteps
going and returning gave mute evidence of the frequency of Leland's
visits. The air was heavy and oppressive and the temperature and
humidity increased as they progressed along the winding length of the
rock-walled passageway. The floor sloped, ever downward and, in spots,
was slippery with slimy seepage. It seemed that they turned back on
their course on several occasions but were descending deeper and
deeper into the heart of the mountain. Then, abruptly, the passage
ended at the mouth of a shaft, which dropped vertically from almost
beneath their feet.

"Whew!" exclaimed Frank. "Another step and I'd have dropped into it.
That's probably what happened to Leland."

He knelt at the rim of the circular opening and looked into the depths
of the pit, Tommy following suit. The feeble ray of the flashlight was
lost in the blackness below.

"Say, Frank," whispered Tommy, "turn off the flash. I think I saw a
light down there."

And, with the snapping of the catch, there came darkness. But, miles
below them, it seemed, there was a tiny pin-point of brilliance--an
eery green light that was like a wavering phosphorescence of
will-o'-the-wisp. For a moment it shone and was gone. Then came the
dreadful vibration they had experienced in the hall of the house--the
whistling scream that grew louder and louder until it seemed they
must be deafened. The penetrating wail rose from the depths of the
pit, and the vibration was all around them, in the damp rock floor on
which they knelt, and in the very air of the cavern. Hastily Frank
snapped on the light of his flash.

"Oh boy!" he whispered. "Leland is certainly up to something down
there and no mistake! How're we going to get down?"

"Get down?" asked Tommy. "You don't want to go down