had awakened him. Not that the chase had led him far in distance. Most
of the time he had spent in waiting just as he was doing now. At first
he had believed that they were searching for something, for they had
ventured into several buildings, each time to emerge conferring, only
to hunt out another and invade it. Since they always returned with
empty hands, he could not believe that they were out for further loot.
Also they moved with more confidence than they had shown the day
before. That confidence led Raf to climb above them so that he could
watch them with less chance of being seen in return.

It had been almost noon when they had at last come into this section.
If two of them had not remained idling on the street as the long
moments crept by, he would have believed that they had given him the
slip, that he was now a cat watching a deserted mouse hole. But at the
moment they were coming back, carrying something.

Raf leaned as far over the parapet as he dared, trying to catch a
better look at the flat, boxlike object two of them had deposited on
the pavement. Whatever it was either needed some adjustment or they
were attempting to open it with poor success, for they had been busied
about it for what seemed an unusually long time. The pilot licked dry
lips and wondered what would happen if he swung down there and just
walked in for a look-see. That idea was hardening into resolution when
suddenly the group below drew quickly apart, leaving the box sitting
alone as they formed a circle about it.

There was a puff of white vapor, a protesting squawk, and the thing
began to rise in jerks as if some giant in the sky was pulling at it
spasmodically. Raf jumped back. Before he could return to his vantage
point, he saw it rise above the edge of the parapet, reach a level
five or six feet above his head, hovering there. It no longer climbed;
instead it began to swing back and forth, describing in each swing a
wider stretch of space.

Back and forth--watching it closely made him almost dizzy. What was
its purpose? Was it a detection device, to locate him? Raf's hand went
to his stun gun. What effect its rays might have on the box he had no
way of knowing, but at that moment he was sorely tempted to try the
beam out, with the oscillating machine as his target.

The motion of the floating black thing became less violent, its swoop
smoother as if some long-idle motor was now working more as its
builders had intended it t