any rate, up until the time of
the Change, which was something the beings of the world could not
stop. It was not a new threat from the lower orders, which they had
met and overcome before, innumerable times. It was not a threat from
outside--no invasion such as they had turned back in the past. Nor was
it a cooling of their world or the danger of imminent collision with
another.

The Change came from within. It was decadence. There was nothing left
for the beings to do. They had solved all their problems and could
find no new ones. They had exhausted the intricate workings of
reflection, academic hypothetica and mind-play; there hadn't been a
new game, for instance, in the lifetime of the oldest inhabitant.

And so they were dying of boredom. This very realization had for a
time halted the creeping menace, because, as they came to accept it
and discuss ways of meeting it, the peril itself subsided. But the
moment they relaxed, the Change started again.

Something had to be done. Mere theorizing about their situation was
not enough. It was then that they sent their spy abroad.

Because they had at one time or another visited each of the planets in
their solar system and had exhausted their possibilities or found them
barren, and because they were not equipped, even at the peak of their
physical development, for intergalactic flight, there remained only
one way to travel--in time.

Not forward or backward, for both had been tried. Travel ahead had
been discouraging--in fact, it had convinced them that their normal
passage through the years had to be stopped. The reason had been made
dramatically clear--they, the master race, did not exist in the
future. They had vanished and the lower forms of life had begun to
take over.

Travel into the past would be even more boring than continued
existence in the present, they realized, because they would be
reliving the experiences they had had and still vividly remembered,
and would be incapable of changing them. It would be both tiresome and
frustrating.

That left only one way to go--sideways in time, across the dimension
line--to a world like their own, but which had developed so
differently through the eons that to visit it and conquer the minds of
its inhabitants would be worth while.

In that way they picked Earth for their victim and sent out their spy.
Just one spy. If he didn't return, they'd send another. There was
enough time. And they had to be sure.