You may get up now," he said. "Slowly, without trying to make trouble."
Val and I helped each other to our feet as best we could, considering
our arms were still tightly bound against the sides of our oxysuits.

"Walk," the stranger said, waving the tanglegun to indicate the
direction. "I'll be right behind you." He holstered the tanglegun.

I glimpsed the bulk of an outboard atomic rigging behind him, strapped
to the back of the wheelchair. He fingered a knob on the arm of the
chair and the two exhaust ducts behind the wheel-housings flamed for a
moment, and the chair began to roll.

Obediently, we started walking. You don't argue with a blaster, even if
the man pointing it is in a wheelchair.

* * * * *

"What's going on, Ron?" Val asked in a low voice as we walked. Behind us
the wheelchair hissed steadily.

"I don't quite know, Val. I've never seen this guy before, and I thought
I knew everyone at the Dome."

"Quiet up there!" our captor called, and we stopped talking. We trudged
along together, with him following behind; I could hear the
_crunch-crunch_ of the wheelchair as its wheels chewed into the sand. I
wondered where we were going, and why. I wondered why we had ever left
Earth.

The answer to that came to me quick enough: we had to. Earth needed
radioactives, and the only way to get them was to get out and look. The
great atomic wars of the late 20th Century had used up much of the
supply, but the amount used to blow up half the great cities of the
world hardly compared with the amount we needed to put them back
together again.

In three centuries the shattered world had been completely rebuilt. The
wreckage of New York and Shanghai and London and all the other ruined
cities had been hidden by a shining new world of gleaming towers and
flying roadways. We had profited by our grandparents' mistakes. They had
used their atomics to make bombs. We used ours for fuel.

It was an atomic world. Everything: power drills, printing presses,
typewriters, can openers, ocean liners, powered by the inexhaustible
energy of the dividing atom.

But though the energy is inexhaustible, the supply of nuclei isn't.
After three centuries of heavy consumption, the supply failed. The
mighty machine that was Earth's industry had started to slow down.

And that started the chain of events that led Val and me to end up as a
madman's prisoners, on Mars. With every source of uranium mined dry