been difficult for anyone to have discerned distinguishing features inside the cumbersome helmets, behind the instruments clamped to the faces of the men who wore the suits. He called no others, but merely watched.

Soon the opaque metal plates of the small lock's outer door had neared to within a few feet of Hawk Carse, and he stopped short, Ban and Friday following suit. They hovered there outside the door, gently swaying like flies against the great gleaming sweep of the dome, the craggy rock face dropping sickeningly down for miles beneath them. And, like flies, they were powerless to open the door to gain entrance. Only the coolie inside could do that; and he, through the dome to one side, was peering at them.

Apparently he was satisfied with his scrutiny. After a moment, bolts shifted and the door stirred and swung out, revealing the all-metal atmosphere chamber and the inner door at the far side. Immediately Carse floated into the chamber, and the two others pressed in behind. They saw the outer door swing shut, and heard its locks thud over.

They were sealed from sight inside the port-lock's atmosphere chamber.

"Looks to me," whispered Ban Wilson, "like a very sweet trap. If that fellow inside wants to—"

The Hawk's cool voice cut him off.

"We can take off the glasses now," he said casually. "Keep alert."

And for a full minute they waited.