Cadet," said one of the first men Tom had
spoken to. "They're building receivers for cargo projectiles."

Tom gulped in surprise. "But how did you know?" he asked.

"Why, it's the only thing we've been talking about down at the garage
and at Sloppy Sam's, the jet-truckers hangout," replied the trucker.
"If this thing works, surface transportation will be finished."

"That's right," asserted another worker. "The whole industry will be
wiped out overnight. Nobody will have anything trucked any more.
Cargo'll be loaded into a projectile and shot off into space to a
passing freighter. Then the freighter carries it to its destination and
shoots it back down to a receiver."

"But how could you know all this?" asked Tom. "It is one of the Solar
Guard's most closely guarded secrets."

"It's all over Mars," declared the truck driver with a derisive laugh.
"Why, everybody knows it."

Suddenly one of the men yelled and pointed toward the fence. The jet
truck parked near the gate was rolling forward slowly. As Tom and the
men watched in horror, the giant vehicle crashed through the fence and
rolled into the restricted area, picking up speed.

In a flash Tom was inside the jet car, driving right through the hole in
the fence and speeding after the huge machine. Around him, guards were
running after the truck, shouting frantic warnings. Far ahead of him,
Tom saw Major Connel and Devers standing near several receivers lined up
outside a blockhouse. The truck was rolling straight toward them.
Hearing the shouts of alarm, the two men turned and saw their danger.
Devers immediately jumped into the safety of the blockhouse, but Connel
stumbled and fell heavily. Tom's blood ran cold. He saw that the major
had struck his head against one of the receivers and he lay on the
ground, dazed and unable to move.

Tom jammed the accelerator of the tiny jet car to the floor and shot
ahead like a rocket. He was alongside the truck now, but the distance
between the huge machine and Connel was narrowing rapidly. Tom clenched
his teeth and urged the little car on faster. He knew that there was not
enough time for him to jump into the truck and pull the brake. There
was only one thing he could do.

Regaining his senses, Connel tried to crawl to safety, but there was no
time. He braced himself for what he knew would be instant death, and
then to his amazement he saw Tom's jet car swerve sharply in front of
the runaway truck.

[Illustration: _