surprised to find out that he knows all about your
pickets and is ready for a raid."

"We'd better rush the place, then," muttered Bolton.

* * * * *

Dr. Bird nodded agreement and with a sharp command to his men Bolton
broke into a run. Not a shot was fired as they approached, and the
front door gave readily to Bolton's touch. At it opened there came a
grating sound from the roof followed by the whir of a propeller. Dr.
Bird ran out of the building and glanced up.

"A helicopter!" he cried. "They were expecting us and have escaped!"

He drew his pistol and fired ineffectually at the great bird-like ship
which was rising almost noiselessly into the air. He cursed and turned
again to the building.

Bolton still stood in the room which they had first entered. His
flashlight showed it to be empty, but from under a door on the
opposite side a line of dull red light glowed evilly. With his pistol
ready in his hand, Bolton approached the door on hands and knees.
When he reached it he threw his shoulder against it and dropped flat
to the floor as the door swung open. No shot greeted him, and he
stared for a moment and then rose to his feet.

"Nothing in here but some glass statues," he announced.

Dr. Bird followed him into the room. As he looked at what Bolton had
called glass statues he gasped and shielded his eyes.

"God in Heaven!" he ejaculated. "Those were living men!"

* * * * *

Before them were three men or what had been three men. All stood in
strained attitudes with a look of horror frozen on their faces. The
thing that made the spectators shudder was that their bodies had, by
some diabolical method, been rendered semi-transparent. The dull red
light which suffused the room emanated from the three bodies. Dr. Bird
examined them closely, being careful not to touch them.

"The identity of my treacherous assistant is known," he said grimly as
he pointed at the middle figure. "It was Gerond. What is this?"

He took an envelope from the hand of the middle figure and opened it.
A sheet of paper fell out and he picked it up and read it.

"My dear Mr. Bolton," ran the note. "Your methods of tracing and
picketing my headquarters are so crude as to be almost laughable. This
base has served its purpose and we were ready to abandon it in any
event, but I couldn't resist the temptation to let you almost nab us.
The three men whom you will find here ar