I + 

Earth Consul, Goodenow, tossed a packet of microfilms to Vanning, and said, “You’re crazy. The man you’re after isn’t here. Only damn fools ever come to Venus⁠—and don’t ask me why I’m here. You’re crazy to think you’ll find a fugitive hiding on this planet.” + 

Jerry Vanning, earth state investigator, moved his stocky body uneasily. He had a headache. He had had it ever since the precarious landing through the tremendous wind-maelstroms of the pea-soup Venusian atmosphere. With an effort he focused his vision on the micro-projector Goodenow handed him, and turned the tiny key. Inside the box, a face sprang into view. He sighed and slid another of the passport-films into place. He had never seen the man before. + 

“Routine checkup,” he said patiently. “I got a tip Callahan was heading here, and we can’t afford to take chances.” + 

The consul mopped his sweating, beefy face and cursed Venusian air-conditioning units. “Who is this guy Callahan, anyway?” he asked. “I’ve heard a little⁠—but we don’t get much news on the frontier.” + 

“Political refugee,” Vanning said, busy with the projector. “Potentially, one of the most dangerous men in the System. Callahan started his career as a diplomat, but there wasn’t enough excitement for him.” + 

The consul fumbled with a cigar. “Can you tell me any more?” + 

“Well⁠—Callahan got hold of a certain secret treaty that must be destroyed. If he shows it in the right places, he might start a revolution, particularly on Callisto. My idea is that he’s hiding out till the excitement dies down⁠—and then he’ll head for Callisto.” + 

Goodenow pursed his lips. “I see. But you won’t find him here.” + 

Vanning jerked his thumb toward a window. “The jungle⁠—” + 

“Hell, no!” the consul said decidedly. “Venus, Mr. Vanning, is not Earth. We’ve got about two hundred settlements scattered here and there; the rest is swamp and mountains. When a man gets lost, we wait a few days and then write out a death certificate. Because once an Earthman leaves a settlement, his number’s up.” + 

“So?” + 

“So Callahan isn’t here. Nobody comes here,” Goodenow said bitterly. + 

“Settlers do,” Vanning remarked. + 

“Bloody fools. They raise herbs and mola. If they didn’t come, Venus would be uninhabited except by natives in a few years. The North-Fever⁠ ⁠… You’d better watch out for that, by the way. If you start feeling rocky, see a doctor. Not that it’ll help. But you can be put under restraint till the fever passes.” + 

Vanning looked up. “I’ve heard of that. Just what⁠—” + 

“Nobody knows,” Goodenow said, shrugging hopelessly. “A virus. A filterable virus, presumably. Scientists have been working on it ever since Venus was colonized. It hits the natives, too. Some get it, some don’t. It works the same way with Earthmen. You feel like you’re cracking up⁠—and then, suddenly⁠—you go North. Into the swamp. You never come back. That’s the end of you.” + 

“Funny!” + 

“Sure it is. But⁠—ever heard of the lemmings? Little animals that used to make mass pilgrimages, millions of them. They’d head west till they reached the ocean, and then keep going. Nobody knew the cause of that, either.” + 

“What lies north?” + 

“Swamp, I suppose. How should I know? We’ve got no facilities for finding out. We can’t fly, and expeditions say there’s nothing there but the usual Venusian hell. I wish⁠—” + 

“Oh-oh!” Vanning sat up, peering into the projector. “Wait a minute, Goodenow. I think⁠—” + 

“Callahan? No!” + 

“He’s disguised, but⁠ ⁠… Lucky this is a three-dimensional movie. Let’s hear his voice.” Vanning touched a button on the box. A low, musical voice said: + 

“My name is Jerome Bentley, New York City, Earth. I’m an importer, and am on Venus to investigate the possibilities of buying a steady supply of herbs⁠—” + 

“Yeah,” Vanning said tonelessly. “That’s it. Jerome Bentley⁠—nuts! That’s Don Callahan! He’s disguised so well his own mother wouldn’t know him⁠—best makeup artist in the System. But I’ve studied his records till I nearly went blind and deaf. I don’t make mistakes about Callahan any more.” + 

Goodenow blinked. “I’ll be blowed. I’ve seen the man a dozen times, and I’d have sworn⁠ ⁠… well! If you’re sure⁠—” + 

“I’m sure.” Vanning referred to the records. “Staying at the Star Palace, eh? Okay, I’ll be pushing off.” + 

“I’ll go with you,” the consul offered, and lifted his bulky body from behind the gleaming desk. Together the two men went out into the muggy Venusian day, which was now fading to a slow, blue dusk. + 

Venus did not revolve; it librated. There was no such thing as sunrise and sunset. But there was a very regular thickening and fading of the eternal cloudbanks that writhed overhead, approximating day and night. Despite the continual frantic disturbance of the atmosphere, the clouds were so thick that it was never possible to see the Sun. + 

Only the ragged, eye-straining movement of the grayness overhead, and the warm, humid wind that gusted against your sweating skin. And the sulphurous smells that drifted in from the jungle⁠—odors of stagnant water and rottenness and things that grew unhealthily white. + 

Frontier town, Vanning thought, as he glanced around. Chicago must have looked like this, in the old days, when streets were unpaved and business was the town’s only reason for existence. But Venus Landing would never grow into another Chicago. A few thousand souls, working under terrible handicaps, always fearing the North-Fever that meant death.⁠ ⁠… + 

Muddy streets, wooden sidewalks already rotting, metal buildings, of two stories at most, long, low hydroponic sheds, a dull, hot apathy that hung over everything⁠—that was Venus Landing. A few natives shuffled past on their snowshoe feet, looking fat and wet, as though made out of wax that had begun to run. + 

The Star Palace was a down-at-the-heels plastic building, stained and discolored by the damp molds. Goodenow jerked his head at the clerk. + 

“Where’s Leester?” + 

“North-Fever,” the man said, worrying his lower lip. “This morning⁠ ⁠… we couldn’t stop him.” + 

“Oh, hell,” the consul said hopelessly, turning to Vanning. “That’s the way it is. Once the fever hits you, you go crazy. Do everything and anything to get away and head north. Leester was a nice kid. He was going back to Earth, next Christmas.” + 

Vanning looked at the clerk. “A man named Jerome Bentley’s staying here.” + 

“He’s somewhere around town. Dunno where.” + 

“Okay,” the consul said. “If he comes in, phone my office. But don’t tell him we were asking.” + 

“Yup.” The clerk resumed his vague scrutiny of the ceiling. Vanning and Goodenow went out. + 

“Where now?” + 

“We’ll just amble around. Hi!” The consul hailed a ricksha, drawn by a native⁠—the usual type of vehicle in Venus Landing’s muddy streets. “Hop in, Vanning.” + 

The detective obeyed. His headache was getting worse. + 

They couldn’t find Callahan. A few men said that they had seen him earlier that day. Someone had glimpsed him on the outskirts of the settlement. + 

“Heading for the jungle?” Goodenow asked quickly. + 

“He⁠—yeah. He looked⁠ ⁠… very bad.” + 

The consul sucked in his breath. “I wonder. Let’s go out that way, Vanning.” + 

“All right. What do you figure⁠—” + 

“The fever, maybe,” Goodenow grunted. “It strikes fast. Especially to non-natives. If your friend Callahan’s caught North-Fever, he just started walking into the swamp and forgot to stop. You can mark the case closed.” + 

“Not till I get that treaty back,” Vanning growled. + 

Goodenow shook his head doubtfully. + 

The buildings grew sparser and ceased at the edge of the pale forest. Broad-leafed jungle growths sprang from moist black soil. The ricksha stopped; the native chattered in his own tongue. + 

“Sure,” Goodenow said, tossing him a coin. “Wait here. Zan-t’kshan.” His burly figure lumbered into the translucent twilight of the jungle. Vanning was at his heels. + 

There were footprints⁠—many of them. The detective ignored them, moving in a straight line away from Venus Landing. Here and there were blazed mola trees, some with buckets hung to collect the dripping sap. The footprints grew fainter. At last only one set remained visible. + 

“A man. Pretty heavyset, too. Wearing Earth shoes, not sandals like most of ours. Callahan, probably.” + 

Vanning nodded. “He didn’t come back by this route.” + 

“He didn’t come back,” Goodenow said shortly. “This is a one-way trail.” + 

“Well, I’m going after him.” + 

“It’s suicidal. But⁠—I suppose I can’t talk you out of it?” + 

“You can’t.” + 

“Well, come back to town and I’ll find you an outfit. Supplies and a hack-knife. Maybe I can find some men willing to go with you.” + 

“No,” Vanning said. “I don’t want to waste time. I’ll start now.” He took a few steps, and was halted by Goodenow’s restraining grip. + 

“Hold on,” the consul said, a new note in his voice. He looked closely into Vanning’s face, and pursed his lips in a soundless whistle. + 

“You’ve got it,” he said. “I should have noticed before.” + 

“Got what?” + 

“The North-Fever, man! Now listen to me⁠—” + 

Vanning’s headache suddenly exploded in a fiery burst of white pain, which washed away and was gone, leaving his brain cool and⁠ ⁠… different. It was like a⁠—like a cold fever. He found his thoughts were moving with unusual clarity to a certain definite point.⁠ ⁠… North. Of course he had to go north. That was what had been wrong with him all day. He had been fighting against the urge. Now he realized that it should be obeyed, instead. + 

He blinked at Goodenow’s heavy, worried face. “I’m all right. No fever. I want to find Callahan, that’s all.” + 

“Like hell it is,” the consul said grimly. “I know the symptoms. You’re coming back with me till you’re well.” + 

“No.” + 

Goodenow made a movement as though to pinion Vanning’s hands behind his back. The detective writhed free and sent a short-arm jab to Goodenow’s jaw. There was power behind that blow. The consul went over backwards, his head thumping against a white tree-bole. + 

He lay still. + 

Vanning didn’t look at the motionless body. He turned and began to follow Callahan’s trail. But he wasn’t watching the footprints. Some instinct seemed to guide him. + 

North⁠ ⁠… North! + 

His head no longer hurt. It felt strangely cool, numb and stinging almost pleasantly. The magnetic pull drew him on. Deeper and deeper into the jungle.⁠ ⁠… + 

Distantly he heard Goodenow’s shout, but ignored it. The consul couldn’t stop him. But he might try. Vanning ran for a while, lightly and easily, till the wilderness of Venus had swallowed him without trace. Then he slowed down to a walk. He would have been grateful for a brief rest, but he could not stop. Not now.⁠ ⁠… + 

The fog closed in. Silver mist veiled the strange, ghostly forest. Then it was torn away as a gust of wind drove down from the upper air. Above, the clouds twisted in tortured writhings; but Vanning did not look up. Not once did he turn his head. He faced north⁠ ⁠… he plodded north⁠ ⁠… he slogged through mushy, stinking swamp that rose at times to his waist.⁠ ⁠… + 

A sane man would have skirted the bog. Vanning floundered across, and swam when he could no longer walk. Somewhere to the left he heard the coughing mutter of a swamp-cat’s engine, but he did not see the machine. His vision was restricted to a narrow circle directly ahead. + 

Dimly he felt pain. The clinging, soft nettles of Venus ripped at his clothing and his skin. Leeches clung to his legs till they fell off, satiated. Vanning went on. He was a robot⁠—an automaton. + 

In silence the pale forest slipped by in a fantastic procession. Lianas often made a tangled snare where Vanning fought for minutes before breaking through. Luckily, the vines had little tensile strength, but soon the man was exhausted and aching in every limb. Far above, the clouds had thickened and darkened into what passed for night on fog-shrouded Venus. But the trees gave a phosphorescent light of their own. Weird beyond imagination was the scene, with the bloody, reeling figure of the man staggering on toward the north⁠— + 

North. Ever north. Until overtaxed muscles refused to bear the burden longer, and Vanning collapsed into exhausted unconsciousness. + 

He did not know when he awoke. Presently he found himself walking again. Nothing had changed. The jungle was denser, and the cool light from above filtered down once more. Only the light was cool. The air itself was sticky and suffocating. + 

He went on into hell. + 

Days and nights merged into a fantastic pattern of dull torture. Some distantly sane portion of his brain held back and watched, but could not help. Days and nights. There was no food. There was water, for as Vanning splashed through shallow pools he would bend his head to drink of the foul liquid. Once his feet crunched on the green-moulded bones of a human skeleton. Others had taken this way before him.⁠ ⁠… + 

Toward the end, a fleshless, gaunt thing that had once been a man dragged itself laboriously toward a range of mountains that lifted from the swamp toward the north. They extended to left and right as far as he could see, and seemed unscalable. But they were V-shaped, and Vanning headed toward the point of the V⁠—the inner point. The terrible drive within him drove him on relentlessly. + 

That night a sulphurous crimson glow lit the sky beyond the mountains. Vanning did not see it. He slept. + 

By morning he was on his way again, staggering into the funnel of the peaks. They were bare rock, eroded by eons of trickling water from the clouds. He could not climb them, even had he possessed the strength. He went on, instead, into the narrowing valley.⁠ ⁠… + 

It ended in a sheer cliff of weathered stone. Vanning reeled toward the barrier. He could not return. The North-Fever drove him on remorselessly. He had to climb that wall of rock, or die. And he could not climb. + 

He fell, rose, and fell again. In the end he crawled. He crawled to the foot of the cliff and dragged himself upright. He fell forward, as though trying to press his body against the towering wall that lifted to the writhing grey clouds⁠— + 

Fell⁠—through the stone! + 

He toppled through the rock curtain as though it were nonexistent! Instantly intense blackness closed around him. Hard stone was under him. + 

His mind was too dulled to wonder. He knew only that the way north was still open. He crept on through darkness, leaving a trail of blood behind him.⁠ ⁠… + 

The ground dropped from under him. He crashed down on a mound of moulded vegetation. + 

Before the shock had passed, the living dead man was moving again. He crawled forward until his way was blocked by a perpendicular wall. Gasping dry-throated sobs, he clawed at the barrier with broken, bleeding fingertips. + 

To left and right, an arm’s length away, were other walls. He was in a pit. The sane part of his brain thought: “Circle around! There may be some way out!” + 

But Vanning could not circle. He could only move in one direction. That was north. He fumbled blindly at the wall, until unconsciousness came at last.⁠ ⁠… + 

Twice again he awoke, each time weaker, and twice again he slept. The fever, having passed its peak, dwindled swiftly. + 

At last Vanning awoke, and he was sane. No longer did he feel the relentless urge to turn north. He lay for a little while staring into the blackness, realizing that he was once more in full command of his traitorous body. + 

There was little life left in him. His tongue was blackened and swollen till it filled his mouth. He was a scarecrow, nearly naked, his bones sharply defined through his skin. + 

It was an effort even to breathe. But death would not be long in coming⁠—now.⁠ ⁠… + 