"Yes, of course. This is a--a valley. The Swamja have lived here for
ages, since before Earthmen colonized Venus."
"I never heard of them."
"None ever return from this place," Lysla said sombrely. "They become
slaves of the Swamja--and in the end they die. New slaves come, as you
did."
Vanning's eyes narrowed. "Hold on. I'm beginning to understand, a
little. The Swamja--those fish-headed people--have a secret city here,
eh? They're intelligent?"
She nodded. "They have great powers. They consider themselves the
gods of Venus. You see--Jerry Vanning--they evolved long before the
anthropoid stock did. Originally they were aquatic. I don't know much
about that. Legends ... Anyway, a very long time ago, they built this
city and have never left it since. But they need slaves. So they send
out the North-Fever--"
* * * * *
"_What?_" Vanning's face grayed. "Lysla--what did you say? The fever's
artificial?"
"Yes. The virus is carried by microscopic spores. The Swamja send it
out to the upper atmosphere, and the great winds carry it all over
Venus. The virus strikes very quickly. Once a man catches it, as you
did, he goes north. These mountains are a trap. They're shaped like a
funnel, so anyone with the fever inevitably heads into the pass, as
you did. They are drawn through the mirage, which looks like a wall of
rock. No one who wasn't--sick--would try to go through that cliff."