when you realize that they learned stellar navigation with
their old system, though most ships use human math now. And of course,
you know their eyes aren't like ours. Among other things, they're
color-blind. They see everything in shades of black or white or gray.

"So they found out that humans aboard their ships were useful. You
remember how humans, in the early days in space, used certain birds, who
were more sensitive to impure air than they were. When the birds keeled
over, they could tell it was time for humans to start looking over the
air systems! The Lhari use Mentorians to identify colors for them. And,
since Mentor was the first planet of humans that the Lhari had contact
with, they've always been closer to them."

Tommy looked after the two Mentorians enviously. "The fact is, I'd ship
out with the Lhari myself if I could. Wouldn't you?"

Bart's mouth twisted in a wry smile. "No," he said. "I could--I'm half
Mentorian, I can even speak Lhari."

"Why don't you? I would."

"Oh, no, you wouldn't," Bart said softly. "Not even very many Mentorians
will. You see, the Lhari don't trust humans too much. In the early days,
men were always planting spies on Lhari ships, to try and steal the
secret of warp-drive. They never managed it, but nowadays the Lhari give
all the Mentorians what amounts to a brainwashing--deep hypnosis, before
and after every voyage, so that they can neither look for anything that
might threaten the Lhari monopoly of space, nor reveal it--even under a
truth drug--if they find it out.

"You have to be pretty fanatical about space travel to go through that.
Oh, my mother could tell us a lot of things about her cruises with the
Lhari. The Lhari can't tell a diamond from a ruby, except by
spectrographic analysis, for instance. And she--"

A high gong note sounded somewhere, touching off an explosion of warning
bells and buzzers all over the enormous building. Bart looked up.

"The ship must be coming in to land."

"I'd better check into the passenger side," Tommy said. He stuck out his
hand. "Well, Bart, I guess this is where we say good-bye."

They shook hands, their eyes meeting for a moment in honest grief. In
some indefinable way, this parting marked the end of their boyhood.

"Good luck, Tom. I'm going to miss you."

They wrung each other's hands again, hard. Then Tommy picked up his
luggage and started down a sloping ramp toward an enclosure marked TO
PASSENGER ENTRANCE.

Warni