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 heavy-set, 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....