y saw the silent, deadly combat up there on the cliff. The two
figures had fallen together from the observatory platform, dropped
twenty feet to a lower landing on the stairs. They lay as though
stunned for a moment, then fought on.

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

"And Haljan," the duty-man gasped. "Went out--something wrong with
Wilks--acting strangely--"

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

"An attack?"

"Is it an attack?"

"The brigands?"

* * * * *

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

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

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

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

He was hastily donning one of the Erentz suits which stood at the lock
entrance. "Shut off that siren, Franck!"

Within a minute Grantline was ready. The duty-man called from the
window:

"Still at it! By the infernal, such fools! They'll kill themselves!"

The figures had swayed back into view, then out of sight again.

"Franck, let me out."

Grantline was ready. He stood, helmet in hand.

"I'll go with you, Commander."

But the volunteer was not equipped. Grantline would not wait.

"I'm going at once. Hurry, Franck."

The duty-man turned to his panel. The volunteer shoved a weapon at
Grantline. "Here, take this."

Grantline jammed on his helmet.

* * * * *

He moved the few steps into the small 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 duty-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 c