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 CO2 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 tricks but one, that were used on the plane I came on, were the same kind of trick. They were all arrangements for getting regular destructive items—bombs or rockets or whatever—where they could explode and smash things. The saboteurs were adding destructive items to various states of things. But there was one trick that was different."
"Yes?" said the Major, on the telephone.
"Putting explosive gas in the CO2 bottles," said Joe painstakingly, "wasn't adding a new gadget to a situation. It was changing something that was already there. The saboteurs took something that belonged in a plane and changed it. They did not put something new into a plane—or a situation—that didn't belong there. It was a special kind of thinking. You see, sir?"
The Major, to do him justice, had the gift of listening. He waited.
"The pushpots," said Joe, very carefully, "naturally have their fuel stored in different tanks in different places, as airplanes do. The pilots switch on one tank or another just like plane pilots. In the underground storage and fueling pits, where all the fuel for the pushpots is kept in bulk, there are different tanks too. Naturally! At the fuel pump, the attendant can draw on any of those underground tanks he chooses."
The Major said curtly: "Obviously! What of it?"
"The pushpot motors explode," said Joe. "And they shouldn't. No bomb could be gotten into them without going off the instant they started, and they don't blow that way. I make a guess, sir, that one of the underground storage tanks—just one—contains doctored fuel. I'm guessing that as separate tanks in a pushpot are filled up, one by one, one is filled from a particular underground storage tank that contains doctored fuel. The rest will have normal fuel. And the pushpot is going to crash when that tank, and only that tank, is used!"
Major Holt was very silent.
"You see, sir?" said Joe uneasily. "The pushpots could be fueled a hundred times over with perfectly good fuel, and then one tank in one of them would explode when drawn on. There'd be no pattern in the explosions…."
Major Holt said coldly: "Of course I see! It would need only one tank of doctored fuel to be delivered to the airfield, and it need not be used for weeks. And there would be no trace in the wreckage, after the fire! You are telling me there is one underground storage tank in which the fuel is highly explosive. It is plausible. I will have it checked immediately."
He hung up, and Joe went back to his meal. He felt uneasy. There couldn't be any way to make a jet motor explode unless you fed it explosive fuel. Then there couldn't be any way to stop it. And then—after the wreck had burned—there couldn't be any way to prove it was really sabotage. But the feeling of having reported only a guess was not too satisfying. Joe ate gloomily. He didn't pay much attention to Talley. He had that dogged, uncomfortable feeling a man has when he knows he doesn't qualify as an expert, but feels that he's hit on something the experts have missed.
Half an hour after the evening mess—near sunset—a security officer wearing a uniform hunted up Joe at the airfield.
"Major Holt sent me over to bring you back to the Shed," he said politely.
"If you don't mind," said Joe with equal politeness, "I'll check that."
He went to the phone booth in the barracks. He got Major Holt on the wire. And Major Holt hadn't sent anybody to get him.
So Joe stayed in the telephone booth—on orders—while the Major did some fast telephoning. It was comforting to know he had a pistol in his pocket, and it was frustrating not to be allowed to try to capture the fake security officer himself. The idea of murdering Joe had not been given up, and he'd have liked to take part personally in protecting himself. But it was much more important for the fake security man to be captured than for Joe to have the satisfaction of attempting it himself.
As a matter of fact, the fake officer started his getaway the instant Joe went to check on his orders. The officer knew they'd be found faked. It had not been practical for him to shoot Joe down where he was. There were too many people around for this murderer to have a chance at a getaway.
But he didn't get away, at that. Twenty minutes later, while Joe still waited fretfully in the phone booth, the phone bell rang and Major Holt was again on the wire. And this time Joe was instructed to come back to the Shed. He had exact orders whom to come with, and they had orders which identified them to Joe.
Some eight miles from the airfield—it was just dusk—Joe came upon a wrecked car with motorcycle security guards working on it. They stopped Joe's escort. Joe's phone call had set off an alarm. A plane had spotted this car tearing away from the airfield, and motorcyclists were guided in pursuit by the plane. When it wouldn't stop—when the fake Security officer in it tried to shoot his way clear—the plane strafed him. So he was dead and his car was a wreck, and the motorcycle men were trying to get some useful information from his body and the car.
Joe went to the Major's house in the officers'–quarters area. The Major looked even more tired than before, but he nodded approvingly at Joe. Sally was there too, and she regarded Joe with a look which was a good deal warmer than her father's.
"You did very well," said the Major detachedly. "I don't have too high an opinion of the brains of anybody your age, Joe. When you are my age, you won't either. But whether you have brains or simply luck, you are turning out to be very useful."
Joe said: "I'm getting security conscious, sir. I want to stay alive."
The Major regarded him with irony.
"I was thinking of the fact that when you worked out the matter of the doctored pushpot fuel, you did not try to be a hero and prove it yourself. You referred it to me. That was the proper procedure. You could have been killed, investigating—it's clear that the saboteurs would be pleased to have a good chance to murder you—and your suspicions might never have reached me. They were correct, by the way. One storage tank underground was half–full of doctored fuel. Rather more important, another was full, not yet drawn on."
The Major went on, without apparent cordiality: "It seems probable that if this particular sabotage trick had not been detected—it seems likely that on the Platform's take–off, all or most of the pushpots would have been fueled to explode at some time after the Platform was aloft, and before it could possibly get out to space."