!"

They had seen the silent, deadly combat up there on the cliff.

Grantline stood stricken with amazement. "That's Wilks!"

"And Haljan," the duty man gasped. "He went out--something wrong with
Wilks' actions--"

The interior of the camp was in a turmoil. The men, awakened from
sleep, ran out into the corridors shouting questions.

"An attack?"

"Is it an attack?"

"The brigands?"

But it was Wilks and Haljan in a fight up there on the cliff. The men
crowded at the bull's-eye windows.

And over all the confusion the alarm siren, with no one thinking to
shut it off, was screaming.

Grantline, momentarily stricken, stood gazing. One of the figures
broke away from the other, bounded up to the summit from the stair
platform to which they had both fallen. The other followed. They
locked together, swaying at the brink. For an instant it seemed that
they would go over; then they surged back, momentarily out of sight.

Grantline found his wits. "Stop them! I'll go out and stop them! What
fools!"

He was hastily donning one of the Erentz suits. "Cut off that siren!"

Within a minute Grantline was ready. The duty man called from the
window, "Still at it, the fools. By the infernal--they'll kill
themselves!"

"Franck, let me out."

"I'll go with you, Commander." But the volunteer was not equipped.
Grantline would not wait.

The duty man turned to his panel. The volunteer shoved a weapon at
Grantline.

Grantline jammed on his helmet, took the weapon.

He moved the few steps into the air chamber which was the first of the
three pressure locks. Its interior door panel swung open for him. But
the door did not close after him!

Cursing the man's slowness, he waited a few seconds. Then he turned to
the corridor. The duty man came running.

Grantline took off his helmet. "What in hell--"

"Broken! Dead!"

"What!"

"Smashed from outside," gasped the duty man. "Look there--my tubes--"

The control tubes of the ports had flashed into a short circuit and
burned out. The admission ports would not open!

"And the pressure controls smashed! Broken from outside!"

There was no way now of getting through the pressure locks. The doors,
the entire pressure lock system, was dead. Had it been tampered with
from outside?

As if to answer Grantline's question there came a chorus of shouts
from the men at the corridor windows.

"Commander! By God--look!"

A figure was outside, close to the building! Clothed in