Baley could sense the vague aroma of Yeast-town growing stronger, more pervasive. He did not find it as unpleasant as some did; Jessie, for instance. He even liked it, rather. It had pleasant connotations.

Every time he smelled raw yeast, the alchemy of sense perception threw him more than three decades into the past. He was a ten-year-old again, visiting his Uncle Boris, who was a yeast farmer. Uncle Boris always had a little supply of yeast delectables: small cookies, chocolaty things filled with sweet liquid, hard confections in the shape of cats and dogs. Young as he was, he knew that Uncle Boris shouldn't really have had them to give away and he always ate them very quietly, sitting in a corner with his back to the center of the room. He would eat them quickly for fear of being caught.

They tasted all the better for that.

Poor Uncle Boris! He had an accident and died. They never told him exactly how, and he had cried bitterly because he thought Uncle Boris had been arrested for smuggling yeast out of the plant. He expected to be arrested and executed himself. Years later, he poked carefully through police files and found the truth. Uncle Boris had fallen beneath the treads of a transport. It was a disillusioning ending to a romantic myth.

Yet the myth would always arise in his mind, at least momentarily, at the whiff of raw yeast.

Yeast-town was not the official name of any part of New York City. It could be found in no gazetteer and on no official map. What was called Yeast-town in popular speech was, to the Post Office, merely the boroughs of Newark, New Brunswick, and Trenton. It was a broad strip across what was once Medieval New Jersey, dotted with residential areas, particularly in Newark Center and Trenton Center, but given over mostly to the many-layered farms in which a thousand varieties of yeast grew and multiplied.

One fifth of the City's population worked in the yeast farms; another fifth worked in the subsidiary industries. Beginning with the mountains of wood and coarse cellulose that were dragged into the City from the tangled forests of the Alleghenies, through the vats of acid that hydrolyzed it to glucose, the carloads of niter and phosphate rock that were the most important additives, down to the jars of organics supplied by the chemical laboratories-it all came to only one thing, yeast and more yeast.

Without yeast, six of Earth's eight billions would starve in a year. Baley felt cold at the thought. Three days before the possibility existed as deeply as it did now, but three days before it would never have occurred to him.

They whizzed out of the motorway through an exit on the Newark outskirts. The thinly populated avenues, flanked on either side by the featureless blocks that were the farms, offered little to act as a brake on their speed.

"What time is it, Daneel?" asked Baley.

"Sixteen-oh-five," replied R. Daneel.

"Then he'll be at work, if he's on day shift."

Baley parked the squad car in a delivery recess and froze the controls.

"This is New York Yeast then, Elijah?" asked the robot.

"Part of it," said Baley.

They entered into a corridor flanked by a double row of offices. A receptionist at a bend in the corridor was instantly smiles. "Whom do you wish to see?"

Baley opened his wallet. "Police. Is there a Francis Clousarr working for New York Yeast?"

The girl looked perturbed. "I can check."

She connected her switchboard through a line plainly marked "Personnel," and her lips moved slightly, though no sound could be heard.

Baley was no stranger to the throat phones that translated the small movements of the larynx into words. He said, "Speak up, please. Let me hear you."

Her words became audible, but consisted only of, "... he says he's a policeman, sir."

A dark, well-dressed man came out a door. He had a thin mustache and his hairline was beginning to retreat. He smiled whitely, and said, "I'm Prescott of Personnel. What's the trouble, Officer?"

Baley stared at him coldly and Prescott's smile grew strained.

Prescott said, "I just don't want to upset the workers. They're touchy about the police."

Baley said, "Tough, isn't it? Is Clousarr in the building now?"

"Yes, Officer."

"Let's have a nod, then. And if he's gone when we get there, I'll be speaking to you again."

The other's smile was quite dead. He muttered, "I'll get you a rod, Officer."

The guide rod was set for Department CG, Section 2. What that meant in factory terminology, Baley didn't know. He didn't have to. The rod was an inconspicuous thing which could be palmed in the hand. Its tip warmed gently when lined up in the direction for which it was set, cooled quickly when turned away. The warmth increased as the final goal was approached.

To an amateur, the guide rod was almost useless, with its quick little differences of heat content, but few City dwellers were amateurs at this particular game. One of the most popular and perennial of the games of childhood was hide-and-seek through the school-level corridors with the use of toy guide rods. ("Hot or Not, Let Hot-Spot Spot. Hot-Spot Guide Rods Are Keen.")

Baley had found his way through hundreds of massive piles by guide rod, and he could follow the shortest course with one of them in his hand as though it had been mapped out for him.

When he stepped into a large and brilliantly lit room after ten minutes, the guide rod's tip was almost hot.

Baley said to the worker nearest the door, "Francis Clousarr here?"

The worker jerked his head. Baley walked in the indicated direction. The odor of yeast was sharply penetrating, despite the laboring air pumps whose humming made a steady background noise.

A man had risen at the other end of the room, and was taking off an apron. He was of moderate height, his face deeply lined despite his comparative youth, and his hair just beginning to grizzle. He had large, knobby hands which he wiped slowly on a celltex towel.

"I'm Francis Clousarr," he said.

Baley looked briefly at R. Daneel. The robot nodded.

"Okay," said Baley. "Anywhere here we can talk?"

"Maybe," said Clousarr slowly, "but it's just about the end of my shift. How about tomorrow?"

"Lots of hours between now and tomorrow. Let's make it now." Baley opened his wallet and palmed it at the yeast farmer.

But Clousarr's hands did not waver in their somber wiping motions. He said, coolly, "I don't know the system in the Police Department, but around here you get tight eating hours with no leeway. I eat at 15:00 to 17:45, or I don't eat."

"It's all right," said Baley. "I'll arrange to have your supper brought to you."

"Well, well," said Clousarr, joylessly. "Just like an aristocrat, or a C-class copper. What's next? Private bath?"

"You just answer questions, Clousarr," said Baley, "and save your big jokes for your girl friend. Where can we talk?"

"If you want to talk, how about the balance room? Suit yourself about that. Me, I've got nothing to say."

Baley thumbed Clousarr into the balance room. It was square and antiseptically white, air-conditioned independently of the larger room (and more efficiently), and with its walls lined with delicate electronic balances, glassed off and manipulable by field forces only. Baley had used cheaper models in his college days. One make, which he recognized, could weigh a mere billion atoms.

Clousarr said, "I don't expect anyone will be in here for a while." Baley grunted, then turned to Daneel and said, "Would you step out and have a meal sent up here? And if you don't mind, wait outside for it."

He watched R. Daneel leave, then said to Clousarr, "You're a chemist?"

"I'm a zymologist, if you don't mind."

"What's the difference?"

Clousarr looked lofty. "A chemist is a soup-pusher, a stink-operator.

A zymologist is a man who helps keep a few billion people alive. I'm a yeast-culture specialist."

"All right," said Baley.

But Clousarr went on, "This laboratory keeps New York Yeast going. There isn't one day, not one damned hour, that we haven't got cultures of every strain of yeast in the company growing in our kettles. We check and adjust the food factor requirements. We make sure it's breeding true. We twist the genetics, start the new strains and weed them out, sort out their properties and mold them again.

"When New Yorkers started getting strawberries out of season a couple of years back, those weren't strawberries, fella. Those were a special high-sugar yeast culture with true-bred color and just a dash of flavor additive. It was developed right here in this room.

"Twenty years ago Saccharomyces olei Benedictae was just a scrub strain with a lousy taste of tallow and good for nothing. It still tastes of tallow, but its fat content has been pushed up from 15 per cent to 87 per cent. If you used the expressway today, just remember that it's greased strictly with S. 0. Benedictae, Strain AG-7. Developed right here in this room.

"So don't call me a chemist. I'm a zymologist."

Despite himself, Baley retreated before the fierce pride of the other. He said abruptly, "Where were you last night between the hours of eighteen and twenty?"

Clousarr shrugged. "Walking. I like to take a little walk after dinner."

"You visited friends? Or a subetheric?"

"No. Just walked."

Baley's lips tightened. A visit to the subetherics would have involved a notch in Clousarr's ration pack. A meeting with a friend would have involved naming a man or woman, and a cross check.

"No one saw you, then?"

"Maybe someone did. I don't know. Not that I know of, though."

"What about the night before last?"

"Same thing."

"You have no alibi then for either night?"

"If I had done anything criminal, Officer, I'd have one. What do I need an alibi for?"

Baley didn't answer. He consulted his little book. "You were up before the magistrate once. Inciting to riot."

"All right. One of the R things pushed past me and I tripped him up. Is that inciting to riot?"

"The court thought so. You were convicted and fined."

"That ends it, doesn't it? Or do you want to fine me again?"

"Night before last, there was a near riot at a shoe department in the Bronx. You were seen there."

"By whom?"

Baley said, "It was at mealtime for you here. Did you eat the evening meal night before last?"

Clousarr hesitated, then shook his head. "Upset stomach. Yeast gets you that way sometimes. Even an old-timer."

"Last night, there was a near riot in Williamsburg and you were seen there."

"By whom?"

"Do you deny you were present on both occasions?"

"You're not giving me anything to deny. Exactly where did these things happen and who says he saw me?"

Baley stared at the zymologist levelly. "I think you know exactly what I'm talking about. I think you're an important man in an unregistered Medievalist organization."

"I can't stop you from thinking, Officer, but thinking isn't evidence. Maybe you know that." Clousarr was grinning.

"Maybe," said Baley, his long face stony, "I can get a little truth out of you right now."

Baley stepped to the door of the balance room and opened it. He said to R. Daneel, who was waiting stolidly outside, "Has Clousarr's evening meal arrived?"

"It is coming now, Elijah."

"Bring it in, will you, Daneel?"

R. Daneel entered a moment later with a metal compartmented tray.

"Put it down in front of Mr. Clousarr, Daneel," said Baley. He sat down on one of the stools lining the balance wall, legs crossed, one shoe swinging rhythmically. He watched Clousarr edge stiffly away as R. Daneel placed the tray on a stool near the zymologist.

"Mr. Clousarr," said Baley. "I want to introduce you to my partner, Daneel Olivaw."

Daneel put out his hand and said, "How do you do, Francis."

Clousarr said nothing. He made no move to grasp Daneel's extended hand. Daneel maintained his position and Clousarr began to redden.

Baley said softly, "You are being rude, Mr. Clousarr. Are you too proud to shake hands with a policeman?"

Clousarr muttered, "If you don't mind, I'm hungry." He unfolded a pocket fork out of a clasp knife he took from his pocket and sat down, eyes bent on his meal.

Baley said, "Daneel, I think our friend is offended by your cold attitude. You are not angry with him, are you?"

"Not at all, Elijah," said R. Daneel.

"Then show that there are no hard feelings. Put your arm about his shoulder."

"I will be glad to," said R. Daneel, and stepped forward.

Clousarr put down his fork. "What is this? What's going on?"

R. Daneel, unruffled, put out his arm.

Clousarr swung backhanded, wildly, knocking R. Daneel's arm to one side. "Damn it, don't touch me."

He jumped up and away, the tray of food tipping and hitting the floor in a messy clatter.

Baley, hard-eyed, nodded curtly to R. Daneel, who thereupon continued a stolid advance toward the retreating zymologist. Baley stepped in front of the door.

Clousarr yelled, "Keep that thing off me."

"That's no way to speak," said Baley with equanimity. "The man's my partner."

"You mean he's a damned robot," shrieked Clousarr.

"Get away from him, Daneel," said Baley promptly.

R. Daneel stepped back and stood quietly against the door just behind Baley. Clousarr, panting harshly, fists clenched, faced Baley.

Baley said, "All right, smart boy. What makes you think Daneel's a robot?"

"Anyone can tell!"

"We'll leave that to a judge. Meanwhile, I think we want you at headquarters, Clousarr. We'd like to have you explain exactly how you knew Daneel was a robot. And lots more, mister, lots more. Daneel, step outside and get through to the Commissioner. He'll be at his home by now. Tell him to come down to the office. Tell him I have a fellow who can't wait to be questioned."

R. Daneel stepped out.

Baley said, "What makes your wheels go round, Clousarr?"

"I want a lawyer."

"You'll get one. Meanwhile, suppose you tell me what makes you Medievalists tick?"

Clousarr looked away in a determined silence.

Baley said, "Jehoshaphat, man, we know all about you and your organization. I'm not bluffing. Just tell me for my own curiosity: What do you Medievalists want?"

"Back to the soil," said Clousarr in a stifled voice. "That's simple, isn't it?"

"It's simple to say," said Baley. "But it isn't simple to do. How's the soil going to feed eight billions?"

"Did I say back to the soil overnight? Or in a year? Or in a hundred years? Step by step, mister policeman. It doesn't matter how long it takes, but let's get started out of these caves we live in. Let's get out into the fresh air."

"Have you ever been out into the fresh air?"

Clousarr squirmed. "All right, so I'm ruined, too. But the children aren't ruined yet. There are babies being born continuously. Get them out, for God's sake. Let them have space and open air and sun. If we've got to, we'll cut our population little by little, too."

"Backward, in other words, to an impossible past." Baley did not really know why he was arguing, except for the strange fever that was burning in his own veins. "Back to the seed, to the egg, to the womb. Why not move forward? Don't cut Earth's population. Use it for export. Go back to the soil, but go back to the soil of other planets. Colonize!"

Clousarr laughed harshly. "And make more Outer Worlds? More Spacers?"

"We won't. The Outer Worlds were settled by Earthmen who came from a planet that did not have Cities, by Earthmen who were individualists and materialists. Those qualities were carried to an unhealthy extreme. We can now colonize out of a society that has built co-operation, if anything, too far. Now environment and tradition can interact to form a new middle way, distinct from either old Earth or the Outer Worlds. Something newer and better."

He was parroting Dr. Fastolfe, he knew, but it was coming out as though he himself had been thinking of it for years.

Clousarr said, "Nuts! Colonize desert worlds with a world of our own at our fingertips? What fools would try?"

"Many. And they wouldn't be fools. There'd be robots to help."

"No," said Clousarr, fiercely. "Never! No robots!"

"Why not, for the love of Heaven? I don't like them, either, but I'm not going to knife myself for the sake of a prejudice. What are we afraid of in robots? If you want my guess, it's a sense of inferiority. We, all of us, feel inferior to the Spacers and hate it. We've got to feel superior somehow, somewhere, to make up for it, and it kills us that we can't at least feel superior to robots. They seem to be better than us - only they're not. That's the damned irony of it."

Baley felt his blood heating as he spoke. "Look at this Daneel I've been with for over two days. He's taller than I am, stronger, handsomer. He looks like a Spacer, in fact. He's got a better memory and knows more facts. He doesn't have to sleep or eat. He's not troubled by sickness or panic or love or guilt.

"But he's a machine. I can do anything I want to him, the way I can to that microbalance right there. If I slam the microbalance, it won't hit me back. Neither will Daneel. I can order him to take a blaster to himself and he'll do it.

"We can't ever build a robot that will be even as good as a human being in anything that counts, let alone better. We can't create a robot with a sense of beauty or a sense of ethics or a sense of religion. There's no way we can raise a positronic brain one inch above the level of perfect materialism.

"We can't, damn it, we can't. Not as long as we don't understand what makes our own brains tick. Not as long as things exist that science can't measure. What is beauty, or goodness, or art, or love, or God? We're forever teetering on the brink of the unknowable, and trying to understand what can't be understood. It's what makes us men.

"A robot's brain must be finite or it can't be built. It must be calculated to the final decimal place so that it has an end. Jehoshaphat, what are you afraid of? A robot can look like Daneel, he can look like a god, and be no more human than a lump of wood is. Can't you see that?"

Clousarr had tried to interrupt several times and failed against Baley's furious torrent. Now, when Baley paused in sheer emotional exhaustion, he said weakly, "Copper turned philosopher. What do you know?"

R. Daneel re-entered.

Baley looked at him and frowned, partly with the anger that had not yet left him, partly with new annoyance.

He said, "What kept you?"

R. Daneel said, "I had trouble in reaching Commissioner Enderby, Elijah. It turned out he was still at his office."

Baley looked at his watch. "Now? What for?"

"There is a certain confusion at the moment. A corpse has been discovered in the Department."

"What! For God's sake, who?"

"The errand boy, R. Sammy."

Baley gagged. He stared at the robot and said in an outraged voice, "I thought you said a corpse."

R. Daneel amended smoothly, "A robot with a completely deactivated brain, if you prefer."

Clousarr laughed suddenly and Baley turned on him, saying huskily, "Nothing out of you! Understand?" Deliberately, he unlimbered his blaster. Clousarr was very silent.

Baley said, "Well, what of it? R. Sammy blew a fuse. So what?"

"Commissioner Enderby was evasive, Elijah, but while he did not say so outright, my impression is that the Commissioner believes R. Sammy to have been deliberately deactivated."

Then, as Baley absorbed that silently, R. Daneel added gravely, "Or, if you prefer the phrase - murdered."