After awhile, he went on to bigger things--whole aircraft, with their
crews, had vanished.

That he had not committed anywhere near all the crimes that had been
attributed to him was certain; that he _had_ committed a great many of
them was equally certain.

There was no doubt at all that his loot was being used to make instruments
and devices of unknown kinds. He had used several of them on his raids.
The one that could apparently phase out almost any electromagnetic
frequency up to about a hundred thousand megacycles--including sixty-cycle
power frequencies--was considered to be a particularly cute item. So was
the gadget that reduced the tensile strength of concrete to about that of
a good grade of marshmallow.

After he had been operating for a few years, there was no installation on
the face of the earth that could be considered Nipe-proof for more than a
few minutes. He struck when and where he wanted and took whatever he
needed.

It was manifestly impossible to guard against the Nipe, since no one knew
what sort of loot might strike his fancy next, and there was therefore no
way of knowing where or how he would hit next.

Nor could he ever be found after one of his raids. They were plotted and
followed out with diabolical accuracy and thoroughness. He struck, looted,
and vanished. And wasn't seen again until his next strike.

Colonel Mannheim, who had carefully puffed a cigar alight and smoked it
thoughtfully during Stanton's recitation, dropped the remains of the cigar
into an ash receptacle. "Accurate but incomplete," he said quietly. "You
must have made some guesses." He looked from Bart Stanton to Dr.
Farnsworth. "I'd like to hear them."

Farnsworth finished off the last of his coffee. "We've talked about it,"
he admitted. "Although I must say the hypothesis Bart has come up with
would never have occurred to me. I'm still not sure I credit it, but" ...
he shrugged ... "I can't say that I disbelieve it, either."

Mannheim turned his eyes back to Stanton. His silence was a question.

"Logically, my theory mightn't hold much water," Stanton admitted. "But
the evidence seems to be conclusive enough to me." He got up, went over to
the coffee urn, and refilled his cup. "It seems incredible to me that the
combined intelligence and organizational ability of the UN Government is
incapable of finding anything out about one single alien, no matter how
competent he may be," he said as he returned to his seat.