ill our way,
just as it must always be. But there must be one exception to this rule:
no one on Earth must be allowed to blunder into the extreme I mentioned
a moment ago."

* * * * *

Tamu, overlord of Mythox, paused to drink from his glass and to cast a
speculative glance at the stolid face of Martin Kirk. He might as well
have studied the contours of a brick wall.

"The road to that blunder had been opened the day your learned men first
split the atom. If they persisted down that path, it was bound to follow
that they would attempt the thing we feared: the splitting of hydrogen
atoms--the hydrogen bomb, as you call it.

"We know what that would mean: a chain reaction that would wipe out an
entire galaxy in one blinding flash. _Our galaxy_, Martin Kirk--yours
and mine! Do you have any thought at all on what that means?"

The question was rhetorical; even before Kirk could shake his head, the
overlord pressed on.

"Mythox and Earth are two grains of dust on opposite sides of a
galaxy--a spiral formation of stars and planets 200,000 light years wide
and 20,000 thick. Between us lie countless other worlds, a vast number
of them supporting life--not always, or even often, life as we know it,
but life nonetheless.

"There is not one of those worlds, Martin Kirk, we do not know as
thoroughly as we do our own. Fortunately for our purpose only a relative
few have progressed along a line which can lead to danger for the rest.
Yours is one of those which has--and that is why we of Mythox have taken
a well-masked place in your affairs _so far as they relate to nuclear
physics_.

"Every scientist of your world, male or female, is constantly under the
eye of a Watcher. These Watchers are members of your own races--people
we have enlisted in the fight to save not just their world or mine--but
millions of worlds.

"When a Watcher learns a physicist is close to the one key to success in
his effort to make a hydrogen bomb--an equation that begins: 'Twelve
times zero point seven nine'--we are notified and a killer from our own
people is sent to execute that scientist. Yes, Martin Kirk, we have
those among us--a very few--who are capable of killing on orders and for
cause. Naia, here, is one of them. She was sent to take the lives of
Gregory Gilmore and Juanita Cordell; but she bungled and instead of
their deaths resembling heart failure, they were obviously murdered.

"Alma Dakin tried to cov