that someone, somehow, was trying
to kill his son.

[Illustration]

It had been late on a Saturday afternoon. The free week-ends that the
Barrier Base engineers had once enjoyed to take their families for
picnics "outside," or to rest and relax, were things of the past, for
the work on the Barrier was reaching a critical stage, demanding more
and more of the technicians, scientists and engineers engaged in its
development. Already diplomatic relations with the Eurasian Combine
were becoming more and more impossible; the Barrier _had_ to be built,
and quickly, or another more terrible New York City would be the
result. Roger had never cleared from his mind the flaming picture of
that night of horror, just five years before, when the mighty
metropolis had burst into radioactive flame, to announce the beginning
of the first Atomic War. The year 2078 was engraved in millions of
minds as the year of the most horrible--and the shortest--war in all
history, for an armistice had been signed not four days after the
first bomb had been dropped. An armistice, but an uneasy peace, for
neither of the great nations had really known what atomic war would be
like until it had happened. And once upon them, they found that atomic
war was not practical, for both mighty opponents would have been
gutted in a matter of weeks. The armistice had stopped the bombs, but
hostilities continued, until the combined scientific forces of one
nation could succeed in preparing a defense.

That particular Saturday afternoon had been busy in the Main Labs on
the Barrier Base. The problem of erecting a continent-long electronic
Barrier to cover the coast of North America was a staggering
proposition. Roger Strang was nearly finished and ready for home as
dusk was falling. Leaving his work at the desk, he was slipping on his
jacket when David came into the lab. He was small for twelve years,
with tousled sand-brown hair standing up at odd angles about a sharp,
intelligent face. "I came to get you, Daddy," he said.

Roger smiled. "You rode all the way down here--just to go home with
me?"

"Maybe we could get some Icy-pops for supper on the way home," David
remarked innocently.

Roger grinned broadly and slapped the boy on the back. "You'd sell
your soul for an Icy-pop," he grinned.

The corridor was dark. The man and boy walked down to the elevator,
and in a moment were swishing down to the dark and deserted lobby
below.

David stepped first fro