The _Sirius_ loafed along through the ether at normal acceleration
just outside the orbit of Mars and a million miles north of the
ecliptic plane. In the control room, which had been transformed into a
bewilderingly complete laboratory, Norman Brandon strode up and down,
waving his arms, his unruly black hair on end, addressing savagely his
friend and fellow-scientist, who sat unmoved and at ease.

"For cat's sake, Quince, let's get busy! They're outside somewhere,
since the police have scoured every cubic kilometer within range of
the power plants without finding a trace of them. We've got the power
question licked right now--with these fields we can draw sixty thousand
kilofranks from cosmic radiation, which is lots more than we'll ever
need. We haven't drawn a frank from a plant in a month, and we've had to
cut our field strength down to a whisper to keep from burning out our
accumulators. We can hunt as far as Neptune easy--we can go to Alpha
Centauri if we want to. This thing of piffling and monkeying around
here's pulling my cork, and for the ten thousand four hundred and sixty
seventh time I say _let's prowl_ and _prowl now_! In fact, I'm getting
so sick of sticking around doing nothing that I'm going out anyway, if
I have to go alone in a lifeboat!"

[Illustration: _The flying fortresses were finally wrenched from the
ground and hurled upward._]

Impetuous and violent as Brandon had always been, never before had he
gone to such lengths as to suggest a disruption of the partnership;
and Westfall, knowing that Brandon, in his most violent moments, never
threatened idly, thought long before he replied.

"You will not go alone, of course. If you insist upon going without
further preparation I will go too, no matter how foolish I think such
a course to be. We have power, it is true, but in all other respects we
are in no condition to meet an opponent having command of such resources
as must certainly be possessed by those who attacked the _Arcturus_.
Our detectors are inefficient, our system of vision is crude, to say
the least, and many other things are still in the experimental stage.
We have not the slightest idea whom or what we may encounter. It is all
too probable that we would simply be throwing away uselessly the lives of
more good men. It is also foolish from a general viewpoint, for as you
already know, we and our assistants happen to be in better position to
study these things than is any one else at