Derec was quivering with tension, but he forced himself to stay clear-headed. “Mandelbrot?”

“I am finding it difficult to concentrate. I am dwelling on this problem and going in circles. If I enter a closed loop on the First Law, I will be useless to you.”

“Now listen to me! Before you go into any kind of closed loop, uh-okay, I’ve got it. Listen.” Derec was talking fast, really before he had more to say. “Urn…”

“I am listening,” said Mandelbrot.

“Maybe ‘u have more information to give ‘irn,” Wolruf suggested. She got down from the chair and stood in front of Mandelbrot, straining her neck to look up at him.

“Yes! That’s it,” said Derec. “Mandelbrot, we’re working with limited information on Ariel. The process she went through was experimental, but I think it worked. I reprogrammed her memory myself. We have to give it a chance.”

“People will have relapses,” Ariel pointed out, in a tightly controlled tone. She was gripping the edge of the desk so hard that her fingertips were white.

“These appear to be similar to a mechanical malfunction,” said Mandelbrot. “Certainly medical care is a logical and customary treatment to facilitate healing.”

“No!” Ariel wailed. “People don’t just fall apart in a straight line like machines. I may be just fine.” Her voice broke at the end, and she blinked back tears, turning away from Mandelbrot.

“I understand,” said Mandelbrot. “Inaction may not necessarily cause further harm to you.”

“Exactly.” Derec let out a long sigh of relief and caught Wolruf’s eyes. She made a face that might have been her version of a wink and then hopped back up on the chair.

“Maybe we can build on that and find out something at the same time,” said Derec. “Mandelbrot, I want to see if your attempts to get information through the city computer are blocked. That will tell us just how special this terminal is. Can you concentrate now on a function of that kind?” Distracting him wouldn’t hurt at the moment.

“Yes, Derec. I judge that the apparent First Law contradiction is still incomplete. The potential loop will close no further unless I receive more evidence that inaction could cause harm.”

“Good.” Derec sat down on the edge of the desk. “Now, last night we found out that the computer would not admit the existence of this office to you. I want to know if that has changed. I ordered it to block all information about our presence here. See if you can call up any hint of our using the facilities here.”

“I am trying several avenues,” said Mandelbrot. His voice was returning to normal. “I’m asking for information about intruders, humans, and energy consumption or oxygen usage in the Compass Tower.”

“What do you get?”

“All is as you instructed,” he answered promptly. “I am told that the office is not listed anywhere. Nor are the water or nutrient tanks in the chemical processor listed. No alerts of any kind have been entered since our arrival.”

“Good!” Derec grinned. “So we really are safe here. Our next problem is to get a line on Avery. Ariel, may I?” He slid off the desk and nodded toward the terminal.

“Of course.” She rose carefully, leaning her fingertips on the desk as though she was worried about her balance.

“Derec,” said Mandelbrot. “I suggest that we attempt parallel work with the city computer. The result should confirm or disprove your suspicions.”

“Good idea. I’ll enter questions and tell you what I’m doing.” Derec seated himself comfortably and started on the keyboard. “All right. How many humans are on the planet of Robot City right now?”

“I learn none,” said Mandelbrot.

“Ha! I’ve got one,” said Derec triumphantly. “Where is this human at the present time?”

“SEATED BEFORE THIS TERMINAL,” said the terminal.

Derec smiled wryly despite his disappointment. “Serves me right,” he muttered. “Wait a minute-” He typed in the question, “How do you know I’m human and not a robot?”

“THE CONSUMPTION OF NUTRIENTS FROM THE CHEMICAL PROCESSOR, USE OF WATER IN THE PERSONAL, AND CHANGES IN THE COMPOSITION OF THE AIR IN THE OFFICE INDICATE THE PRESENCE OF AT LEAST ONE HUMAN. THE PROBABILITY OF THE PRESENCE OF MORE THAN ONE HUMAN BASED ON THE AMOUNT OF HEAT GENERATED IN THE ROOM IS HIGH. COMBINING THIS FACT WITH THE ABILITY OF ROBOTS TO CONTACT THE CITY COMPUTER DIRECTLY THROUGH THEIR COMLINKS INDICATES THE PROBABILITY THAT YOU ARE HUMAN.”

Derec felt a twinge of panic. “So the use of this office has been recorded in the computer, after all?” His fingers fumbled on the keys, and he had to retype the question twice.

“NO.”

“Explain your knowledge of this information, then.”

“INFORMATION FROM THIS OFFICE IS STORED IN LOCAL MEMORY AT THIS TERMINAL. IT HAS NOT BEEN SENT TO THE CITY CENTRAL COMPUTER, PER YOUR INSTRUCTION.”

“Is the information in your local memory available to anyone else, anywhere?”

“NEGATIVE.”

Derec relaxed then, rubbing his fingertips against each other. At some point, he would no longer be able to use the keys. Someone else could handle the keyboard if necessary, but that would mean admitting his disability.

“What’s wrong?” Ariel asked.

“False alarm.” Derec placed his fingers back on the keyboard and thought a moment. Then he entered, “What other locations indicate similar evidence of human presence on this planet?”

“NONE.”

“I’m not surprised.” He looked at the others. “Wherever our paranoid friend is hiding, he had the presence of mind to keep that information unavailable, even here.”

“Maybe especially here,” said Ariel, “if he was expecting us to search this office.”

“Maybe ‘e lefft,” suggested Wolruf. “Used a Key to leave the planet entirrely.”

“Oh, no.” Ariel looked from her to Derec. “You don’t think he left Robot City, do you? How can we find him then?”

Derec set his jaw grimly. “Wherever he is, we have to pick up his trail here.”

“But if he has kept all the information out of the computer, we won’t have any to find.” Ariel’s voice was cracking again.

Wolruf moved to her side in a silent offer of moral support.

“Mandelbrot,” said Derec. “Find out if any humans have been treated at that medical facility. If you can think of any more avenues for reaching evidence of humans on the planet, go ahead and follow them. And if you don’t get any results, let me try.”

“Yes, Derec.”

Derec put his hands on the keyboard again and missed the first two keys he tried. “Wait a minute. We can shortcut this. Mandelbrot, you sit down at this terminal and use it.” He got up carefully, looking at Ariel and Mandelbrot to see if they had noticed his mistakes on the keyboard. If so, they did not show it.

Wolruf was eyeing him closely, but she said nothing. Instead, she left Ariel’s side and took a position where she could watch the screen as Mandelbrot worked on it.

“Mandelbrot,” said Derec, “turn on the viewscreens.” He turned to face one wall, hands on hips.

A moment later, the little office was flooded with light. On all sides, Robot City bustled on the ground far below them, stretching away until it vanished over the horizon. Above them, the sky shone down with brilliant sunlight.

Ariel turned slowly, as though in awe. “I don’t recognize any of it,” she said softly.

Derec saw towers, spires, swirls, and loops in the architecture he had never seen here before, either. Humanoid and function robots moved about on the streets and on vehicles or machinery everywhere. He remembered that single-rnindedness, that sense of purpose, from the asteroid where he had first seen the Avery robots.

Circuit Breaker, the distinctive structure that had revealed the ability of Robot City robots to think and dream creatively, was gone.

“The changes are extensive,” said Derec. “It’s not your memory at fault right now.”