away as Joe's face showed how he felt. But of course there were the
orders that said he was a sabotage expert. And Joe felt angrily that he
was sailing under false colors. He didn't know anything about sabotage.
He believed that he was probably the least qualified of anybody that
security had ever empowered to look into methods of destruction.

Yet, in a sense, that very fact was an advantage. A man may be set to
work to contrive methods of sabotage. Another man may be trained to
counter him. The training of the second man is essentially a study of
how the first man's mind works. Then it can be guessed what this
saboteur will think and do. But such a trained security man will often
be badly handicapped if he comes upon the sabotage methods of a second
man--an entirely different saboteur who thinks in a new fashion. The
security man may be hampered in dealing with the second man's sabotage
just because he knows too much about the thinking of the first.

Joe went off and scowled at a wall, while the young lieutenant waited
hopefully nearby.

He was in a false position. But he could see that there was something
odd here. There was a sort of pattern in the way the other sabotage
incidents had been planned. It was hard to pick out, but it was there.
Joe thought of the trick of booby-trapping a plane during its major
overhaul, and then arming the traps at a later date.... A private plane
had been fitted to deliver proximity rockets in mid-air when the
transport ship flew past. There was the explosion of the cargo parcel
which was supposed to contain requisition forms and stationery. And the
attempt to smash the entire Platform by getting an atomic bomb into a
plane and having a saboteur shoot the crew and then deliver the bomb at
the Shed in an officially harmless aircraft....

The common element in all those sabotage tricks was actually clear
enough, but Joe wasn't used to thinking in such terms. He did know,
though, that there was a pattern in those devices which did not exist in
the blowing up of jet motors from inside.

He scowled and scowled, racking his brains, while the young lieutenant
watched respectfully, waiting for Joe to have an inspiration. Had Joe
known it, the lieutenant was deeply impressed by his attempt at
concentration on the problem it had not been Major Holt's intention for
Joe to consider. When Joe temporarily gave up, the young lieutenant
eagerly showed him over the whole field and all its workings