Without positronic brains, the function robots could not set the controls, so only humans and robots with positronic brains rode the booths. Derec observed, as he watched the robots speed past, that they all stood motionless and staring straight ahead, unlike humans, who of course would be shifting positions, shuffling their feet, and looking around. The robots were logical, but never curious.

Ahead of them, several robots were emerging from platform booths. Derec and Ariel split up to approach them.

Derec stood directly in front of one to make sure the robot could see him clearly as a human in the dim light. “Just a moment. I would like to ask you a few questions.”

“Yes?” The robot stopped.

“Have you seen any humans?”

“I presume you mean other than yourself.”

“Yeah, besides me.”

“Your companion is a female human.”

“Besides us!”Derec flung up his hands. “Somewhere else in the city. Anywhere.”

“No. You are the first humans I have ever seen.”

“Thanks.” Derec sighed and flagged down another robot. “Have you seen any humans other than my companion and myself?”

“What companion?”

“Uh-her. Over there. See her?”

“Yes.”

“You have? Where?”

“Over there. Where you pointed.”

“What-no, not her-”

“You asked if I saw her. I said yes.”

“Okay, okay. Now, then. Other than the two of us present right here, have you ever seen any humans on Robot City?”

“No.”

“All right, thanks.” Derec waved him on.

At the moment, no more robots were coming into the siding loop or down the ramp. Ariel joined him.

“No luck here,” she said. “You get anything?”

“No. Let’s ride out to the Key Center.”

They got into the first empty booth. It was a fairly close fit, but not uncomfortable. Derec set the controls and the booth started with a slight jolt.

The platform carried them along the siding loop slowly, so that it could merge smoothly onto the first track at the earliest opening. Derec’s trust in the engineering job done by the robots was so great that he never worried about safety. If the robots themselves had any doubts about the system, the First Law would have forced them to keep the humans from riding in it.

He didn’t know exactly how the platforms were powered, though it must have been through the tracks. In a city where construction was rampant, these details often came and went so fast that learning them just didn’t matter. The platforms moved quickly, with a faint hum, and never seemed to need sudden changes in speed.

At Ariel’s suggestion, they got off at a couple of tunnel stops to question more robots, but this random search continued to produce nothing. They emerged from the system as close to the Key Center as they could, but still some distance away. In order to go on questioning robots on the street, they took the slidewalk, though they did not learn anything new this way, either.

When they first came into view of the dome, Derec stopped short. A huge opening gaped in the curving surface, and gigantic pieces of machinery, some easily ten and fifteen meters high, were being driven into the dome on a flatbed vehicle. More robots were visible inside than before, possibly to install the new equipment.

“If they were people,” said Derec, “I’d try to get inside during the confusion. The trouble is, 1 don’t see any confusion. They know what they’re doing. I don’t think there’s much point in trying to sneak in right now.”

“Let’s move along.” She took his arm and steered him away. “No sense alerting Keymo’s security to the fact that we’re back.”

“True.”

They began to walk a discreet perimeter around the dome, making further inquiries of robots they met. The lack of information made it clear that the strangers had simply not been there.

“They will be,” said Ariel. “They have to come here for the Key sooner or later. Suppose we instruct all the robots in the neighborhood to report sightings directly to us on the console.”

“We can try,” he said doubtfully. “The way the city keeps expanding, their population shifts all the time.”

They continued their perimeter, now adding the instruction that the robots report sightings directly to them, and also to the central computer under the heading of “alien presences.” When they had completed the circuit, Derec found himself gazing with hands on hips at the seamless wall of the Key Center, where the big opening was now fully sealed and scarless.

“This walking around talking just isn’t getting us anywhere,” Derec said. “Looking for our mysterious strangers is all right, but if we leave Robot City, we can forget about them anyhow. We can’t get around it. We have to get inside the dome and get one of those keys.”

“I’m afraid you’re right. Look, I owe you on this one. Come on, let’s do it. Do you remember where you left your boot?”

“Yeah, over there.”

“You get over to it. I’m going to provide the diversion you needed the last time, over at the opposite side.”

“No good. I won’t know when to enter unless I can see you.”

“All right-I’ll stand just in sight. That way the curve of the dome will help keep the security robot from seeing you.”

“Its name is Security 1K.”

He walked over to the spot where a portion of his boot was still protruding from the wall, and waved to her. In response, she pounded on the wall.

“Hey! Open up in there! This is a human order!”

She did not, however, step back. With both fists on her hips and her feet wide apart, she stood with her toes right up against the wall of the dome.

The wall opened, as before, with a tearing sound right in front of her. Security 1K started to step out, but when she held her ground, the robot remained where it was. Derec could just barely see its hands moving. The robot was going to see him from that spot.

“We have learned that three other humans are present on the planet of Robot City,” Ariel began. “We must speak with Keymo. These humans may endanger us.”

Derec did not wait any longer. He pulled the boot just loose enough to get a hold of the free edges of dianite. When he began to pull gently, it ripped apart without much noise.

Inside the dome, everything was different. The floor was crammed with machinery, some of it even larger than the pieces he had seen entering a while before. Other units were quite compact.

He noted thankfully that the spaces between many of them offered him room to maneuver without being in anyone’s line of sight, at least as long as Ariel kept Security 1K occupied. As carefully as he could, he crawled and scooted through the dark passages between machines, away from the robots he could see working here and there. This gradually moved him to a side of the building where he was able to peek out across the floor.

Now that the new machines had been installed, the crew in the dome was down to normal numbers again. They seemed more crowded in the smaller space remaining to them, but, as usual, they were efficiently concentrating on their tasks. That single-minded dedication helped Derec move unnoticed.

He caught sight of the security seat on its high perch. From where he was now, he could not see if Ariel was still keeping Security 1K busy, but that console was too inviting to pass up. Still moving cautiously, he reached the bottom of the perch.

The lift was a smaller version of those he had seen on the asteroid, and a version of the tunnel booths. A smaller lever lowered the entire seat, and, once he was in it, a button on the arm raised it. The seat moved up until it was just beneath the ceiling he had observed on his first visit. At the summit, he found himself looking out over the entire floor, with a complex array of controls and displays in front of him.

Not a single robot looked up at him. To one side, Security 1K stood with his back to the interior of the building, still talking with Ariel. Derec concentrated on the displays.