There's A Wolf In My Time Machine 
By Larry Niven.
The old extension cage had no fine controls, but that hardly mattered. It wasn't as if Svetz were chasing some particular extinct animal. Ra Chen had told him to take whatever came to hand.
Svetz guided the cage back to Pre-industrial America, somewhere in mid-continent, around 1000 Ante-Atomic Era. Few humans, many animals. Perhaps he'd find a bison.
And when he pulled himself to the window, he looked out upon a vast white land.
Svetz had not planned to arrive in midwinter.
Briefly he considered moving into the time stream again and using the interrupter circuit. Try another date, try the luck again. But the interrupter circuit was new, untried, and Svetz wasn't about to be the first man to test it.
Besides which, a trip into the past cost over a million commercials. Using the interrupter circuit would nearly double that. Ra Chen would be displeased.
Svetz began freezing to death the moment he opened the door. From the doorway the view was all white, with one white bounding shape far away.
Svetz shot it with a crystal of soluble anesthetic.
He used the flight stick to reach the spot. Now that it was no longer moving, the beast was hard to find. It was just the color of the snow, but for its open red mouth and the black pads on its feet. Svetz tentatively identified it as an arctic wolf.
It would fit the Vivarium well enough. Svetz would have settled for anything that would let him leave this frozen wilderness. He felt uncommonly pleased with himself. A quick, easy mission.
Inside the cage, he rolled the sleeping beast into what might have  been a clear plastic bag, and sealed it. He strapped the wolf against one curved wall of the extension cage. He relaxed into the curve of the opposite wall as the cage surged in a direction vertical to all directions.
Gravity shifted oddly.
A transparent sac covered Svetz's own head. Its lip was fixed to the skin of his neck. Now Svetz pulled it loose and dropped it. The air system was on; he would not need the filter sac.
The wolf would. It could not breath industrial-age air. Without the filter sac to remove the poisons, the wolf would choke to death. Wolves were extinct in Svetz's time.
Outside, time passed at a furious rate. Inside, time crawled. Nestled in the spherical curve of the extension cage, Svetz stared up at the wolf, who seemed fitted into the curve of the ceiling.
Svetz had never met a wolf in the flesh. He had seen pictures in children's books ... and even the children's books had been stolen from the deep past. Why should the wolf look so familiar?
It was a big beast, possibly as big as Hanville Svetz, who was a slender, small-boned man. Its sides heaved with its panting. Its tongue was long and red, and its teeth were white and sharp.
Like the dogs, Svetz remembered. The dogs in the Vivarium, in the glass case labeled: 
DOG Contemporary 
Alone of the beasts in the Vivarium, the dogs were not sealed in glass for their own protection. The others could not breath the air outside. The dogs could.
In a very real sense, they were the work of one man. Lawrence Wash Porter had lived near the end of the Industrial Period, between 50 and 100 Post-Atomic Era, when billions of human beings were dying of lung diseases while scant millions adapted. Porter had decided to save the dogs.
Why the dogs? His motives were obscure, but his methods smacked of genius. He had acquired members of each of the breeds of dog in the world and bred them together over many generations of dogs and most of his own lifetime.
There would never be another dog show. Not a purebred dog was left in the world. But hybrid vigor had produced a new breed. These, the ultimate mongrels, could breath industrial-age air, rich in oxides of carbon and nitrogen, scented with raw gasoline and sulfuric acid.
The dogs were behind glass because people were afraid of them. Too many species had died. The people of 1100 Post-Atomic were not used to animals.
Wolves and dogs ... could one have sired the other?
Svetz looked up at the sleeping wolf and wondered. He was both like and unlike the dogs. The dogs had grinned out through the glass and wagged their tails when children waved. Dogs liked people. But the wolf, even in sleep...
Svetz shuddered. Of all the things he hated about his profession, this was the worst: the ride home, staring up at a strange and dangerous extinct animal. The first time he'd done it, a captured horse had seriously damaged the control panel. On his last mission an ostrich had kicked him and broken three ribs.
The wolf was stirring restlessly ... and something about it had changed.
Something was changing now. The beast's snout was shorter, wasn't it? Its forelegs lengthened peculiarly; its paws seemed to grow and spread.
Svetz caught his breath, and instantly forgot the wolf. Svetz was choking, dying. He snatched up his filter sac and threw himself at the controls.
Svetz stumbled out of the extension cage, took three steps, and collapsed. Behind him, invisible contaminants poured into the open air.
The sun was setting in banks of orange cloud.
Svetz lay where he had fallen, retching, fighting for air. There was an outdoor carpet beneath him, green and damp, smelling of plants. Svetz did not recognize the smell, did not at once realize that the carpet was alive. He would not have cared at that point. He knew only that the cage's air system had tried to kill him. The way he felt, it had probably succeeded.
It had been a near thing. He had been passing 30 Post-Atomic when the air went bad. He remembered clutching the interrupter switch, then waiting, waiting. The foul air stank in his nostrils and caught in his throat and tore at his larynx. He had waited through twenty years, feeling every second of them. At 50 Post-Atomic he had pulled the interrupter switch and run choking from the cage.
50 PA. At least he had reached industrial times. He could breathe the air.
It was the horse, he thought without surprise. The horse had pushed its wickedly pointed horn through Svetz's control panel, three years ago. Maintenance was supposed to fix it. They had fixed it.
Something must have worn through.
The way he looked at me every time I passed his cage. I always knew the horse would get me, Svetz thought.
He noticed the filter sac still in his hand. Not that he'd be-
Svetz sat up suddenly.
There was green all about him. The damp green carpet beneath him was alive; it grew from the black ground. A rough, twisted pillar thrust from the ground, branched into an explosion of red and yellow papery things. More of the crumpled colored paper lay about the pillar's base. Something that was not an aircraft moved erratically overhead, a tiny thing that fluttered and warbled.
Living, all of it. A pre-industrial wilderness.
Svetz pulled the filter sac over his head and hurriedly smoothed the edges around his neck to form a seal. Blind luck that he hadn't fainted yet. He waited for it to puff up around his head. A selectively permeable membrane, it would pass the right gasses in and out until the composition of the air was- was- Svetz was choking, tearing at the sac.
He wadded it up and threw it, sobbing. First the air plant, now the filter sac! Had someone wrecked them both? The inertial calendar too: he was at least a hundred years previous to 50 Post-Atomic.
Someone had tried to kill him.
Svetz looked wildly about him. Uphill across a wide green carpet, he saw an angular vertical-sided formation painted in shades of faded green. It had to be artificial. There might be people there. He could-
No, he couldn't ask for help either. Who would believe him? How could they help him anyway? His only hope was the extension cage. And his time must be very short.
The extension cage rested a few yards away, the door a black circle on one curved side. The other side seemed to fade away into nothing. It was still attached to the rest of the time machine, in 1103 PA, along a direction eyes could not follow.
Svetz hesitated near the door. His only hope was to disable the air plant. Hold his breath, then-
The smell of contaminants was gone.
Svetz sniffed at the air. Yes, gone. The air plant had exhausted itself, drained its contaminants into the open air. No need to wreck it now. Svetz was sick with relief.
He climbed in.
He remembered the wolf when he saw the filter sac, torn and empty. Then he saw the intruder towering over him, the coarse thick hair, the yellow eyes glaring, the taloned hands spread wide to kill.
The land was dark. In the east a few stars showed, though the west was still deep red. Perfumes tinged the air. A full moon was rising.
Svetz staggered uphill, bleeding.
The house on the hill was big and old. Big as a city block, and two floors high. It sprawled out in all directions, as though a mad architect had built to a whim that changed moment by moment. There were wrought-iron railings on the upper floor windows, and wrought-iron handles on the screens on both floors, all painted the same dusty shade of green. The screens were wood, painted a different shade of green. They were closed across every window. No light leaked through anywhere.
The door was built for someone twelve feet tall. The knob was huge. Svetz used both hands and put all his weight into it, and still it would not turn. He moaned. He looked for the lens of a peeper camera and could not find it. How would anyone know he was here? He couldn't find a doorbell either.
Perhaps there was nobody inside. No telling what this building was. It was far too big to be a family dwelling, too spread out to be a hotel or apartment house. Might it be a warehouse or a factory? Making or storing what?
Svetz looked back toward the extension cage. Dimly he caught the glow of the interior lights. He also saw something moving on the living green that carpeted the hill.
Pale forms, more than one.
Moving this way?
Svetz pounded on the door with his fists. Nothing. He noticed a golden metal thing, very ornate, high on the door. He touched it, pulled at it, let it go. It clanked.
He took it in both hands and slammed the knob against its base again and again. Rhythmic clanking sounds. Someone should hear it.
Something zipped past his ear and hit the door hard. Svetz spun around, eyes wild, and dodged a rock the size of his fist. The white shapes were nearer now. Bipeds, walking hunched.
They looked too human-or not human enough.
The door opened.
She was young, perhaps sixteen. Her skin was very pale, and her hair and brows were pure white, quite beautiful. Her garment covered her from neck to ankles, but left her arms bare. She seemed sleepy and angry as she pulled the door open- manually, and it was heavy, too. Then she saw Svetz.
"Help me," said Svetz.
Her eyes went wide. Her ears moved too. She said something Svetz had trouble interpreting, for she spoke in ancient american.
"What are you?"
Svetz couldn't blame her. Even in good condition his clothes would not fit the period. But his blouse was ripped to the navel, and so was his skin. Four vertical parallel lines of blood ran down his face and chest.
Zeera had been coaching him in the american speech. Now he said carefully, "I am a traveler. An animal, a monster, has taken my vehicle away from me."
Evidently the sense came through. "You poor man! What kind of animal?"
"Like a man, but hairy all over; with a horrible face-and claws-claws-"
"I see the marks they made."
"I don't know how he got in. I-" Svetz shuddered. No, he couldn't tell her that. It was insane, utterly insiine, this conviction that Svetz's wolf had become a bloodthirsty humanoid monster. "He only hit me once. On the face. I could get him out with a weapon, I think. Have you a bazooka?"
"What a funny word! I don't think so. Come inside. Did the trolls bother you?" She took his arm and pulled him in and shut the door.
Trolls?
"You're a strange person," the girl said, looking him over. "You look strange, you smell strange, you move strangely. I did not know that there were people like you in the world. You must come from very far away."
"Very," said Svetz. He felt himself close to collapse. He was safe at last, safe inside. But why were the hairs on the back of his neck trying to stand upright?
He said, "My name is Svetz. What's yours?"
"Wrona." She smiled up at him, not afraid despite his strangeness ... and he must look strange to her, for she surely looked strange to Hanville Svetz. Her skin was sheet white, and her rich white hair would better have fit a centenarian.
Her nose, very broad and flat, would have disfigured an ordinary girl. Somehow it fit Wrona's face well enough; but her face was most odd, and her ears were too large, almost pointed, and her eyes were too far apart, and her grin stretched way back ... and Svetz liked it. Her grin was curiosity and enjoyment, and was not a bit too wide. The firm pressure of her hand was friendly, reassuring. Though her fingernails were uncomfortably long and sharp.
"You should rest, Svetz," she said. "My parents will not be up for another hour, at least. Then they can decide how to help you. Come with me, I'll take you to a spare room."
He followed her through a room dominated by a great rectangular table and a double row of high-backed chairs. There was a large microwave oven at one end, and beside it a platter of ... red things. Roughly conical they were, each about the size of a strong man's upper arm, each with a dot of white in the big end. Svetz had no idea what they were; but he didn't like their color. They seemed to be bleeding.
"Oh," Wrona exclaimed. "I should have asked. Are you hungry?"
Svetz was, suddenly. "Have you dole yeast?"
"Why, I don't know the word. Are those dole yeast? They are all we have."
"We'd better forget it." Svetz's stomach lurched at the thought of eating something that color. Even if it turned out to be a plant.
Wrona was half supporting him by the time they reached the room. It was rectangular and luxuriously large. The bed was wide enough, but only six inches off the floor, and without coverings. She helped him down to it. "There's a wash basin behind that door, if you find the strength. Best you rest, Svetz. In perhaps two hours I will call you."
Svetz eased himself back. The room seemed to rotate. He heard her go out.
How strange she was. How odd he must look to her. A good thing she hadn't called anyone to tend him. A doctor would notice the differences.
Svetz had never dreamed that primitives would be so different from his own people. During the thousand years between now and the present, there must have been massive adaptation to changes in air and water, to DDT and other compounds in foods, to extinction of food plants and meat animals until only dole yeast was left, to higher noise levels, less room for exercise, greater dependence on medicines... Well, why shouldn't they be different? It was a wonder humanity had survived at all.
Wrona had not feared his strangeness, nor cringed from the scratches on his face and chest. She was only amused and interested. She had helped him without asking too many questions. He liked her for that.
He dozed.
Pain from deep scratches, stickiness in his clothes made his sleep restless. There were nightmares. Something big and shadowy, half man and half beast, reached far out to slash his face. Over and over. At some indeterminate time he woke completely, already trying to identify a musky, unfamiliar scent.
No use. He looked about him, at a strange room that seemed even stranger from floor level. High ceiling. One frosted globe, no brighter than a full moon, glowed so faintly that the room was all shadow. Wrought-iron bars across the windows; black night beyond.
A wonder he'd wakened at all. The pre-industrial air should have killed him hours ago.
It had been a futz of a day, he thought. And he shied away from the memory of the thing in 'the extension cage. Snarling face, pointed ears, double row of pointed white teeth. The clawed hand reaching out, swiping down. The nightmare conviction that a wolf had turned into that.
It could not be. Animals did not change shape like that. Something must have gotten in while Svetz was fighting for air. Chased the wolf out, or killed it.
But there were legends of such things, weren't there? Two and three thousand years old and more, everywhere in the world, were the tales of men who could become beasts and vice versa.
Svetz sat up. Pain gripped his chest, then relaxed. He stood up carefully and made his way to the bathroom.
The spigots were not hard to solve. Svetz wet a cloth with warm water. He watched himself in the mirror, emerging from under the crusted blood. A pale, slender young man topped with thin blond hair ... and an odd distortion of chin and forehead. That must be the mirror, he decided. Primitive workmanship. It might have been worse. Hadn't the first mirrors been two-dimensional?
A shrill whistle sounded outside his door. Svetz went to look, and found Wrona. "Good, you're up," she said. "Father and Uncle Wrocky would like to see you."
Svetz stepped into the hall, and again noticed the elusive musky scent. He followed Wrona down the dark hallway. Like his room, it was lit only by a single white frosted globe. Why would Wrona's people keep the house so dark? They had electricity.
And why were they all sleeping at sunset? With breakfast laid out and waiting...
Wrona opened a door, gestured him in.
Svetz hesitated a step beyond the threshold. The room was as dark as the hallway. The musky scent was stronger here. He jumped when a hand closed on his upper arm-it felt wrong; there was hair on the palm; the hard nails made a circlet of pressure points-and a gravelly male voice boomed, "Come in. Mister Svetz. My daughter tells me you're a traveler in need of help."
In the dim light Svetz made out a man and a woman seated on backless chairs. Both had hair as white as Wrona's, but the woman's hair bore a broad black stripe. A second man urged Svetz toward another backless chair. He too bore black markings: a single black eyebrow, a black crescent around one ear.
And Wrona was just behind him.
Svetz looked around at them all, seeing how alike they were, how different from Hanville Svetz.
The fear rose up in him like a strong drug. Svetz was a xenophobe.
They were all alike. Rich white hair and eyebrows, black markings. Narrow black fingernails. The broad flat noses and the wide, wide mouths, the sharp white conical teeth, the high, pointed ears that moved, the yellow eyes, the hairy palms.
Svetz dropped heavily onto the padded footstool.
One of the males noticed: the larger one, who was still standing. "It must be the heavier gravity," he guessed. "It's true, isn't it, Svetz? You're from another world. Obviously you're not quite a man. You told Wrona you were a traveler, but you didn't say from how far away."
"Very far," Svetz said weakly, "From the future."
The smaller male was jolted. "The future? You're a time traveler?" His voice became a snarl. "You're saying that we will evolve into something like you!"
Svetz cringed. "No. Really."
"I hope not. What, then?"
"I think I must have gone sidewise in time. You're descended from wolves, aren't you? Not apes. Wolves."
"Yes, of course."
The seated male was looking him over. "Now that he mentions it, he does look much more like a troll than any man has a right to. No offense intended, Svetz."
Svetz, surrounded by wolf men, tried to relax. And failed. "What is a troll?"
Wrona perched on the edge of his stool. "You must have seen them on the lawn. We keep about thirty."
"Plains apes," the smaller male supplied. "Imported from Africa, sometime in the last century. They make good watch-beasts and meat animals. You have to be careful with them, though. They throw things."
"Introductions," the other said suddenly. "Excuse our manners, Svetz. I'm Flakee Wrocky. This is my brother Flakee Worrel, and Brenda, his wife. My niece you know."
"Pleased to meet you," Svetz said hollowly.
"You say you slipped sideways in time?"
"I think so. A futz of a long way, too," said Svetz. "Marooned. Gods protect me. It must have been the horse-"
Wrocky broke in. "Horse?"
"The horse. Three years ago, a horse damaged my extension cage. It was supposed to be fixed. I suppose the repairs just wore through, and the cage slipped sideways in time instead of forward. Into a world where wolves evolved instead of Homo habilis. Gods know where I'm likely to wind up if I try to go back."
Then he remembered. "At least you can help me there. Some kind of monster has taken over my extension cage."
"Extension cage?"
"The part of the time machine that does the moving. You'll help me evict the monster?"
"Of course," said Worrel, at the same time that the other was saying, "I don't think so. Bear with me, please, Worrel. Svetz, it would be a disservice to you if we chased the monster out of your extension cage. You would try to reach your own time, would you not?"
"Futz, yes!"
"But you would only get more and more lost. At least in our world you can eat the food and breathe the air. Yes, we grow food plants for the trolls; you can learn to eat them."
"You don't understand. I can't stay here. I'm a xenophobe!"
Wrocky frowned. His ears flicked forward enquiringly. "What?"
"I'm afraid of intelligent beings who aren't human. I can't help it. It's in my bones."
"Oh, I'm sure you'll get used to us, Svetz."
Svetz looked from one male to the other. It was obvious enough who was in charge. Wrocky's voice was much louder and deeper than Worrel's; he was bigger than the other man, and his white fur fell about his neck in a mane like a lion's. Worrel was making no attempt to assert himself. As for the women, neither had spoken a word since Svetz entered the room.
Wrocky was emphatically the boss. And Wrocky didn't want Svetz to leave.
"You don't understand," Svetz said desperately. "The air-" He stopped.
"What about the air?"
"It should have killed me by now. A dozen times over. In fact, why hasn't it?" Odd enough that he'd ever stopped wondering about that. "I must have adapted," Svetz said half to himself. "That's it. The cage passed too close to this line of history. My heredity changed. My lungs adapted to pre-industrial air. Futz it! If I hadn't pulled the interrupter switch, I'd have adapted back."
"Then you can breath our air," said Wrocky.
"I still don't understand it. Don't you have any industries?"
"Of course," Worrel said in surprise.
"Internal-combustion cars and aircraft? Diesel trucks and ships? Chemical fertilizers, insect repellents-"
"No, none of that. Chemical fertilizers wash away, ruin the water. The only insect repellents I ever heard of smelted to high heaven. They never got beyond the experimental stage. Most of our vehicles are battery powered."
"There was a fad for internal-combustion once," said Wrocky. "It didn't spread very far. They stank. The people inside didn't care, of course, because they were leaving the stink behind. At its peak there were over two hundred cars tootling around the city of Detroit, poisoning the air. Then one night the citizenry rose in a pack and tore all the cars to pieces. The owners too."
Worrel said,  "I've always thought that men have more sensitive noses than trolls."
"Wrona noticed my smell long before I noticed hers. Wrocky, this is getting us nowhere. I've got to go home. I seem to have adapted to the air, but there are other things. Foods: I've never eaten anything but dole yeast; everything else died out long ago. Bacteria."
Wrocky shook his head. "Anywhere you go, Svetz, your broken time machine will only take you to more and more exotic environments. There must be a thousand ways the world could end. Suppose you stepped out into one of them? Or just passed near one?"
"But-"
"Here, on the other paw, you will be an honored guest. Think of all the things you can teach us! You, who were born into a culture that builds time-traveling vehicles!"
So that was it. "Oh, no. You couldn't use what I know," said Svetz. "I'm no mechanic. I couldn't show you how to do anything. Besides, you'd hate the side effects. Too much of past civilizations was built on petrochemicals. And plastics. Burning plastics produces some of the strangest-"
"But even the most extensive oil reserves could not last forever. You must have developed other power sources by your own time."
Wrocky's yellow eyes seemed to bore right through him. "Controlled hydrogen fusion?"
"But I can't tell you how it's done!" Svetz cried desperately. "I know nothing of plasma physics!"
"Plasma physics? What are plasma physics?"
"Using electromagnetic fields to manipulate ionized gasses. You must have plasma physics."
"No, but I'm sure you can give us some valuable hints. Already we have fusion bombs. And so do the Europeans ... but we can discuss that later." Wrocky stood up. His black nails made pressure points on Svetz's arm. "Think it over, Svetz. Oh, and make yourself free of the house, but don't go outside without an escort. The trolls, you know."
Svetz left the room with his head whirling. The wolves would not let him leave.
"Svetz, I'm glad you're staying," Wrona chattered. "I like you. I'm sure you'll like it here. Please let me show you over the house."
Down the length of the hallway, one frosted globe burned dimly in the gloom, like a full moon transported indoors. Nocturnal, they were nocturnal.
Wolves.
"I'm a xenophobe," he said. "I can't help it. I was born that way."
"Oh, you'll learn to like us. You like me a little already, don't you, Svetz?" She reached up to scratch him behind the ear. A thrill of pleasure ran through him, unexpectedly sharp, so that he half closed his eyes.
"This way," she said.
"Where are we going?"
"I thought I'd show you some trolls. Svetz, are you really descended from trolls? I can't believe it!"
"I'll tell you when I see them," said Svetz. He remembered the Homo habilis in the Vivarium. It had been a man, an Advisor, until the Secretary-General ordered him regressed.
They went through the dining room, and Svetz saw unmistakable bones on the plates. He shivered.
His forebears had eaten meat; the trolls were brute animals here, whatever they might be in Svetz's world-but Svetz shuddered. His thinking seemed turgid, his head felt thick. He had to get out of here.
"If you think Uncle Wrocky's tough, you should meet the European ambassador," said Wrona.
"Perhaps you will."
"Does he come here?"
"Sometimes." Wrona growled low in her throat. "I don't like him. He's a different species, Svetz. Here it was the wolves that evolved into men; at least that's what our a teacher tells us. In Europe it was something else."
"I don't think Uncle Wrocky will let me meet him. Or even tell him about me." Svetz rubbed at his eyes.
"You're lucky. Herr Dracula smiles a lot and says nasty things in a polite voice. It takes you a minute to-Svetz! What's wrong?"
Svetz groaned like a man in agony. "My eyes!" He felt higher.
"My forehead! I don't have a forehead any more!"
"I don't understand."
Svetz felt his face with his fingertips. His eyebrows were a caterpillar of hair on a thick, solid ridge of bone. From the brow ridge his forehead sloped back at forty-five degrees. And his chin, his chin was gone too. There was only a regular curve of jaw into neck.
"I'm regressing. I'm turning into a troll," said Svetz. "Wrona, if I turn into a troll, will they eat me?"
"I don't know. I'll stop them, Svetz!"
"No. Take me down to the extension cage. If you're not with me, the trolls will kill me."
"All right. But, Svetz, what about the monster?"
"He should be easier to handle by now. It'll be all right. Just take me there. Please."
"All right, Svetz." She took his hand and led him.
The mirror hadn't lied. He'd been changing even then, adapting to this line of history. First his lungs had lost their adaption to normal air. There had been no industrial age here. But there had been no Homo sapiens either...
Wrona opened the door. Svetz sniffed at the night. His sense of smell had become preternaturally acute. He smelled the trolls before he saw them, coming uphill toward him across the living green carpet. Svetz's fingers curled, wishing for a weapon.
Three of them. They formed a ring around Svetz. and Wrona. One of them carried a length of white bone. They all walked upright on two legs, but they walked as if their feet hurt them. They were as hairless as men. Apes' heads mounted on men's bodies.
Homo habilis, the killer plains ape. Man's ancestor.
"Pay them no attention," Wrona said offhandedly. "They won't hurt us." She started down the hill. Svetz followed closely.
"He really shouldn't have that bone," she called back. "We try to keep bones away from them. They use them as weapons. Sometimes they hurt each other. Once one of them got hold of the iron handle for the lawn sprinkler and killed a gardener with it."
"I'm not going to take it away from him."
"That glaring light, is that your extension cage?"
"Yes."
"I'm not sure about this, Svetz."
She stopped suddenly. "Uncle a Wrocky's right. You'll only get more lost. Here you'll at least be taken care of."
"No. Uncle Wrocky was wrong. See the dark side of the extension cage, how it fades away to nothing? It's still attached to the rest of the time machine. It'll just reel me in."
"Oh."
"No telling how long it's been veering across the time lines. Maybe ever since that futzy horse poked his futzy horn through the controls. Nobody ever noticed before. Why should they? Nobody ever stopped a time machine halfway before."
"Svetz, horses don't have horns."
"Mine does."
There was noise behind them.
Wrona looked back into a darkness Svetz's eyes could not pierce.
"Somebody must have noticed us! Come on, Svetz!"
She pulled him toward the lighted cage. They stopped just outside.
"My head feels thick," Svetz mumbled. "My tongue too."
"What are we going to do about the monster? I can't hear anything-" 
"No monster. Just a man with amnesia, now. He was only dangerous in the transition stage."
She looked in. "Why, you're right! Sir, would you mind-Svetz, he doesn't seem to understand me."
"Sure not. Why should he? He thinks he's a white arctic wolf." Svetz stepped inside. The white-haired wolf man was backed into a corner, warily watching. He looked a lot like Wrona.
Svetz became aware that he had picked up a tree branch. His hand must have done it without telling his brain. He circled, holding the weapon ready. An unreasoning rage built up and up in him. Invader! The man had no business here in Svetz's territory.
The wolf man backed away, his slant eyes mad and frightened. Suddenly he was out the door and running, the trolls close behind.
"Your father can teach him, maybe," said Svetz.
Wrona was studying the controls. "How do you work it?"
"Let me see. I'm not sure I remember." Svetz rubbed at his drastically sloping forehead. "That one closes the door-" Wrona pushed it. The door closed.
"Shouldn't you be outside?"
"I want to come with you," said Wrona.
"Oh." It was getting terribly difficult to think. Svetz looked over the control panel. Eeny, meeny- that one? Svetz pulled it.
Free fall. Wrona yipped. Gravity came, vectored radially outward from the center of the extension cage. It pulled them against the walls.
"When my lungs go back to normal, I'll probably go to sleep," said Svetz. "Don't worry about it." Was there something else he ought to tell Wrona? He tried to remember.
Oh, yes. "You can't go home again," said Svetz. "We'd never find this line of history again."
"I want to stay with you," said Wrona.
"All right."
Within a deep recess in the bulk of the time machine, a fog formed. It congealed abruptly-and Svetz's extension cage was back, hours late. The door popped open automatically. But Svetz didn't come out.
They had to pull him out by the shoulders, out of air that smelled of beast and honeysuckle.
"He'll be all right in a minute. Get a filter tent over that other thing," Ra Chen ordered. He stood over Svetz with his arms folded, waiting.
Svetz began breathing.
He opened his eyes.
"All right," said Ra Chen. "What happened?"
Svetz sat up. "Let me think. I went back to pre-industrial America. It was all snowed in. I ... shot a wolf."
"We've got it in a tent. Then what?"
"No. The wolf left. We chased him out." Svetz's eyes went wide.
"Wrona!"
Wrona lay on her side in the filter tent. Her fur was thick and rich, white with black markings. She was built something like a wolf, but more compactly, with a big head and a short muzzle and a tightly curled tail. Her eyes were closed. She did not seem to be breathing.
Svetz knelt. "Help me get her out of there! Can't you tell the difference between a wolf and a dog"
"No. Why would you bring back a dog, Svetz? We've got dozens of dogs."
Svetz wasn't listening. He pulled away the filter tent and bent over Wrona. "I think she's a dog. More dog than wolf, anyway. People tend to domesticate each other. She's adapted to our line of history. And our brand of air." Svetz looked up at his boss. "Sir, we'll have to junk the old extension cage. It's been veering sideways in time."
"Have you been eating gunchy pills on the job?"
"I'll tell you all about it-"
Wrona opened her eyes. She looked about her in rising panic until she found Svetz. She looked up at him, her golden eyes questioning.
"I'll take care of you. Don't worry," Svetz told her. He scratched her behind the ear, his fingertips deep in soft fur. To Ra Chen he said, "The Vivarium doesn't need any more dogs. She can stay with me."
"Are you crazy, Svetz? You, live with an animal? You hate animals!"
"She saved my life. I won't let anyone put her in a cage," he said determinedly.
"Sure, keep it! Live with it! I don't suppose you plan to pay back the two million commercials she cost us? I thought not." Ra Chen made a disgusted sound. "All right, let's have your report. And keep that thing under control, will you?"
Wrona raised her nose and sniffed at the air. Then she howled. The sound echoed within the Institute, and heads turned in questioning and fear.
Puzzled, Svetz imitated the gesture, and understood.
The air was rich with petrochemicals and oxides of carbon and nitrogen and sulfur. Industrial air, the air Svetz had breathed all his life.
And Svetz hated it.