A cold wind moved through the air, eddying against him. In the forming gray light the trees and hills were beginning to take shape, a hard, unbending outline. He turned toward the city. Bleak and thin, the shafts of the deserted buildings stuck up. For a moment he watched, fascinated by the first color of day as it struck the shafts and towers. Then the color faded, and a drifting mist moved between him and the city. All at once he bent down and grabbed up his load. He began to walk, hurrying as best he could, chill fear moving through him.

From the city a black speck had leaped up into the sky and was hovering over it.

After a time, a long time, Hasten looked back. The speck was still there—but it had grown. And it was no longer black; in the clear light of day the speck was beginning to flash, shining with many colors.

He increased his pace; he went down the side of a hill and up another. For a second he paused to snap on his click-band. It spoke loudly; he was not far from the sphere. He waved his arm and the clicks rose and fell. To the right. Wiping the perspiration from his hands he went on.

A few minutes later he looked down from the top of a ridge and saw a gleaming metal sphere resting silently on the grass, dripping with cold dew from the night. The Time Car; sliding and running, he leaped down the hill toward it.

He was just pushing the door open with his shoulder when the first cloud of butterflies appeared at the top of the hill, moving quietly toward him.

He locked the door and set his armload down, flexing his muscles. His hand ached, burning now with an intense pain. He had no time for that—he hurried to the window and peered out. The butterflies were swarming toward the sphere, darting and dancing above him, flashing with color. They began to settle down onto the metal, even onto the window. Abruptly, his gaze was cut off by gleaming bodies, soft and pulpy, their beating wings mashed together. He listened. He could hear them, a muffled, echoing sound that came from all sides of him. The interior of the sphere dimmed into darkness as the butterflies sealed off the window. He lit the artificial lights.

Time passed. He examined the newspapers, uncertain of what to do. Go back? Or ahead? Better jump ahead fifty years or so. The butterflies were dangerous, but perhaps not the real thing, the lethal factor that he was looking for. He looked at his hand. The skin was black and hard, a dead area was increasing. A faint shadow of worry went through him; it was getting worse, not better.

The scratching sound on all sides of him began to annoy him, filling him with an uneasy restlessness. He put down the books and paced back and forth. How could insects, even immense insects such as these, destroy the human race? Surely human beings could combat them. Dusts, poisons, sprays.

A bit of metal, a little particle drifted down onto his sleeve. He brushed it off. A second particle fell, and then some tiny fragments. He leaped, his head jerking up.

A circle was forming above his head. Another circle appeared to the right of it, and then a third. All around him circles were forming in the walls and roof of the sphere. He ran to the control board and closed the safety switch. The board hummed into life. He began to set the indicator panel, working rapidly, frantically. Now pieces of metal were dropping down, a rain of metal fragments onto the floor. Corrosive, some kind of substance exuded from them. Acid? Natural secretion of some sort. A large piece of metal fell; he turned.

Into the sphere the butterflies came, fluttering and dancing toward him. The piece that had fallen was a circle of metal, cut cleanly through. He did not have time even to notice it; he snatched up the blowtorch and snapped it on. The flame sucked and gurgled. As the butterflies came toward him he pressed the handle and held the spout up. The air burst alive with burning particles that rained down all over him, and a furious odor reeked through the sphere.

He closed the last switches. The indicator lights flickered, the floor chugged under him. He threw the main lever. More butterflies were pushing in, crowding each other eagerly, struggling to get through. A second circle of metal crashed to the floor suddenly, emitting a new horde. Hasten cringed, backing away, the blowtorch up, spouting flame. The butterflies came on, more and more of them.

Then sudden silence settled over everything, a quiet so abrupt that he blinked. The endless, insistent scratching had ceased. He was alone, except for a cloud of ashes and particles over the floor and walls, the remains of the butterflies that had got into the sphere. Hasten sat down on the stool, trembling, he was safe, on his way back to his own time; and there was no doubt, no possible doubt that he had found the lethal factor. It was there, in the heap of ashes on the floor, in the circles neatly cut in the hull of the car. Corrosive secretion? He smiled grimly.

His last vision of them, of the swelling horde had told him what he wanted to know. Clutched carefully against the first butterflies through the circles were tools, tiny cutting tools. They had cut their way in, bored through; they had come carrying their own equipment.

He sat down, waiting for the Time Car to complete its journey.

Department guards caught hold of him, helping him from the Car. He stepped down unsteadily, leaning against them. “Thanks,” he murmured.

Wood hurried up. “Hasten, you’re all right?”

He nodded. “Yes. Except my hand.”

“Let’s get inside at once.” They went through the door, into the great chamber. “Sit down.” Wood waved his hand impatiently, and a soldier hurried a chair over. “Get him some hot coffee.”

Coffee was brought. Hasten sat sipping. At last he pushed the cup away and leaned back.

“Can you tell us now?” Wood asked.

“Yes.”

“Fine.” Wood sat down across from him. A tape recorder whirred into life and a camera began to photograph Hasten’s face as he talked. “Go on. What did you find?”

When he had finished the room was silent. None of the guards or technicians spoke.

Wood stood up, trembling. “God. So it’s a form of toxic life that got them. I thought it was something like that. But butterflies? And intelligent. Planning attacks. Probably rapid breeding, quick adaptation.”

“Maybe the books and newspapers will help us.”

“But where did they come from? Mutation of some existing form? Or from some other planet. Maybe space travel brought them in. We’ve got to find out.”

“They attacked only human beings,” Hasten said. “They left the cows. Just people.”

“Maybe we can stop them.” Wood snapped on the vidphone. “I’ll have the Council convene an emergency session. We’ll give them your description and recommendations. We’ll start a program, organize units all over the planet. Now that we know what it is, we have a chance. Thanks to you, Hasten, maybe we can stop them in time!”

The operator appeared and Wood gave the Council’s code letter. Hasten watched dully. At last he got to his feet and wandered around the room. His arm throbbed unmercifully. Presently he went back outside, through the doorway into the open square. Some soldiers were examining the Time Car curiously. Hasten watched them without feeling, his mind blank.

“What is it, sir?” one asked.

“That?” Hasten roused himself, going slowly over. “That’s a Time Car.”

“No, I mean this.” The soldier pointed to something on the hull. “This, sir; it wasn’t on there when the Car went out.”

Hasten’s heart stopped beating. He pushed past them, staring up. At first he saw nothing on the metal hull, only the corroded metal surface. Then chill fright rushed through him.

Something small and brown and furry was there, on the surface. He reached out, touching it. A sack, a stiff little brown sack. It was dry, dry and empty. There was nothing in it; it was open at one end. He stared up. All across the hull of the Car were little brown sacks, some still full, but most of them already empty.