een overlaid by these other sights and Joe could think of
his next meal without aversion. When it was evening-mess time he went
doggedly back to the mess hall. There was a sort of itchy feeling in his
mind. He knew something he didn't know he knew. There was something in
his memory that he couldn't recall.

Talley and Walton were again at mess. Joe went to their table. Talley
looked at him inquiringly.

"Yes, I saw both crashes," said Joe gloomily, "and I didn't want any
lunch. It was sabotage, though. Only it was different in kind--it was
different in principle--from the other tricks. But I can't figure out
what it is!"

"Mmmmmm," said Talley, amiably. "You'd learn something if you could talk
to the Resistance fighters and saboteurs in Europe. The Poles were
wonderful at it! They had one chap who could get at the tank cars that
took aviation gasoline from the refinery to the various Nazi airfields.
He used to dump some chemical compound--just a tiny bit--into each
carload of gas. It looked all right, smelled all right, and worked all
right. But at odd moments Hitler's planes would crash. The valves would
stick and the engine'd conk out."

Joe stared at him. And it was just as simple as that. He saw.

"The Nazis lost a lot of planes that way," said Talley. "Those that
didn't crash from stuck valves in flight--they had to have their valves
reground. Lost flying time. Wonderful! And when the Nazis did uncover
the trick, they had to re-refine every drop of aviation gas they had!"

Joe said: "That's it!"

"That's it? And _it_ is what?"

Then Joe said disgustedly: "Surely! It's the trick of loading CO_2
bottles with explosive gas, too! Excuse me!"

He got up from the table and hurried out. He found a phone booth and got
the Shed, and then the security office, and at long last Major Holt. The
Major's tone was curt.

"Yes?... Joe?... The three men from the affair of the lake were tracked
this morning. When they were cornered they tried to fight. I am afraid
we'll get no information from them, if that's what you wanted to know."

The Major's manner seemed to disapprove of Joe as expressing curiosity.
His words meant, of course, that the three would-be murderers had been
fatally shot.

Joe said carefully: "That wasn't what I called about, sir. I think I've
found out something about the pushpots. How they're made to crash. But
my hunch needs to be checked."

The Major said briefly: "Tell me."

Joe said: "All the