cle. We've only been
here two years, you know. The iceworms must all have been asleep when
we came. But they came swarming out of the ice by the hundreds last
month."

"How come Earth doesn't know?"

"The antenna for our long-range transmitter was outside the Dome. One of
the worms came by and chewed the antenna right off. All we've got left
is this short-range thing we're using and it's no good more than ten
thousand miles from here. You're the first one who's been this close
since it happened."

"I get it." Preston closed his eyes for a second, trying to think things
out.

* * * * *

The Colony was under blockade by hostile alien life, thereby making it
impossible for him to deliver the mail. Okay. If he'd been a regular
member of the Postal Service, he'd have given it up as a bad job and
gone back to Earth to report the difficulty.

_But I'm not going back. I'll be the best damned mailman they've got._

"Give me a landing orbit anyway, Ganymede."

"But you can't come down! How will you leave your ship?"

"Don't worry about that," Preston said calmly.

"We have to worry! We don't dare open the Dome, with those creatures
outside. You _can't_ come down, Postal Ship."

"You want your mail or don't you?"

The colonist paused. "Well--"

"Okay, then," Preston said. "Shut up and give me landing coordinates!"

There was a pause, and then the figures started coming over. Preston
jotted them down on a scratch-pad.

"Okay, I've got them. Now sit tight and wait." He glanced contemptuously
at the three mail-pouches behind him, grinned, and started setting up
the orbit.

_Mailman, am I? I'll show them!_

* * * * *

He brought the Postal Ship down with all the skill of his years in the
Patrol, spiralling in around the big satellite of Jupiter as cautiously
and as precisely as if he were zeroing in on a pirate lair in the
asteroid belt. In its own way, this was as dangerous, perhaps even more
so.

Preston guided the ship into an ever-narrowing orbit, which he
stabilized about a hundred miles over the surface of Ganymede. As his
ship swung around the moon's poles in its tight orbit, he began to
figure some fuel computations.

His scratch-pad began to fill with notations.

_Fuel storage--_

_Escape velocity--_

_Margin of error--_

_Safety factor--_

Finally he looked up. He had computed exactly how much spare fuel he
had, how much he coul