On their third orbit, Jacob located their destination: the beleaguered robot city Wohler-9 had described by radio after they had jumped into the system. Derec was apparently not in the city at the time. Ariel had counted on hearing Derec's voice.

Their destination was the second-largest iridescent domed pit they had seen on the planet, and the only one with a pie-cut of city buildings that extended to the center of the shimmering pit.

Jacob laid in a trajectory that would bring them through the atmosphere to a landing on the open plain half a kilometer north of the dome and near the path of evacuation of the Avery robots; and then, with the help of the jumper's computer, he executed the maneuver flawlessly. They disembarked less than fifty meters from the line of evacuation and commandeered a large courier robot carrying two packages.

“Return to the city;' Ariel said as she sat down on one of the packages and motioned Jacob to sit down on the other one. She would like to have said, “Take me to Wohler,” but the non-positronic brain of the courier would not have been capable of interpreting and executing that command.

As they neared the open sector of the dome, towering a kilometer above them, Ariel said, “Can you raise Wohler on the radio, Jacob?”

“I have, Miss Ariel,” Jacob replied. “He is standing over to the right of the opening in the dome.” The robot pointed and said, “There by that large open lorry.”

Up close, the paradoxical nature of the huge iridescent bubble became more dramatic as Ariel looked down through the flickering wall of the dome into a pit that seemed to underlie a city built on solid ground. Looking through the wall and the opening at the same time, the city seemed to float above the excavation. It left her feeling decidedly uneasy.

“Take us to Wohler,” she said to the courier. They disembarked at the lorry and walked up to Wohler-9, an imposing gold machine standing at the front of the lorry and facing the stream of evacuating robots.

“I am Ariel Welsh,” she said.

“I know,” said Wohler-9.

“What is going on here?” Ariel asked.

“We are moving the necessary materiel for construction of a second Compass Tower and city on the other side of the plain, five kilometers away.”

“Why?”

“This dome will soon be closed by the aliens, blocking all traffic into and out of the city.”

“Why?”

“That is not clear.”

“Where is Derec Avery?”

“I do not know, since he is not on this planet.”

Ariel took a moment to absorb that. “When did he leave?”

“He has never been here,” the golden robot replied.

Now she felt slightly ill. She had misunderstood that weak relay from a central computer, which had led her to believe Derec would be here. She had to keep talking, or scream. She had thought she would see him so soon.

“Are all the supervisors here ninth generation?” she asked.

“No. I am the only ninth. All others are eighth generation.”

“How did that come about?”

“Wohler-l sacrificed himself to rescue you from the side of Robot City's Compass tower during a life-threatening thunderstorm, Miss Welsh.”

The Burundi's Fever Dr. Avery had exposed her to-amnemonic plague, so-called-had robbed her of the links to her memory. The memory had still been there, but she had lost the connections to it. Derec had helped restore those links by providing clues from their mutual experiences. That particular experience involving Wohler-l must have been exceptionally potent, for now her mind orchestrated that clue into an unnerving symphony of emotion as the experience condensed into consciousness. The guilt of causing the termination of that magnificent golden robot, laid on top of her misunderstanding of the relayed message from this planet, left her momentarily faint.

She swallowed hard to regain her composure and then said brusquely, “What is the nature of the dome? Why not simply destroy it?”

“A simple demonstration will suffice to answer your question, Miss Welsh,” Wohler-9 replied.

He unclipped a meter-long, chrome-plated crowbar from the side of the lorry and started walking toward the edge that bordered the right side of the opening in the dome's glimmer.

Ariel and Jacob followed him, and as Ariel approached the interior of the dome, getting a little ahead of Wohler-9 in her impetuous fashion, she could see up close the soft blackness of the lining, a blackness that demarcated the end of the ground and the beginning of what seemed open space. Looking down at it sent her into a dizzying subjective vertigo. She seemed to spin in that black space as it drew her down, sucking at her mind.

“Under no circumstances come closer than half a meter, Miss Welsh,” Wohler-9 said as he casually moved his arm in front of her. With that warning she seemed to come to her senses, and she moved back out so that she was facing the edge from a distance of a few meters; her head cleared, and from that position she could now see along both the inside and outside walls.

Wohler-9 then approached the edge of the wall to almost that half-meter limit himself. He stopped then, facing the inner wall, and said; “And don't become confused. The wall may seem deceptively far away. “

He took a baseball batter's stance then, and with a lusty swing that brought the crowbar around in a horizontal arc perpendicular to the wall, he struck the edge of the dome with the middle of the crowbar. Without a sound, the edge of the dome, like the edge of a supersharp tool, cut the crowbar neatly in half. The far end of the crowbar sailed off. The near end stayed firmly in Wohler-9's hands as he completed his swing.

Then he casually tossed the remnant toward the inside wall.

Ariel's eyes had naturally followed the flight of the far end of the crowbar until it hit the ground and stopped skidding. She looked back just as Wohler-9 tossed the piece left in his hand toward the interior blackness.

That piece seemed to curve in toward the blackness a fraction of the distance it would have traveled if he had tossed it straight up in the air with the same force, and then it came shooting back out on a parabolic course obviously calculated to hit no one. It landed behind him a distance equal to the distance it would have traveled in front of him if the wall had not been there.

“Now, a second demonstration will point up and clarify the dome's external characteristics,” Wohler-9 said.

He picked up the half-crowbar that had just sailed back out of the blackness, walked over, tossed it into the lorry, and then unclipped two sections of a tubular pole from the side of the vehicle. When he fitted the two sections together, he had a pole about five meters long. From a locker he took a large piece of white cloth that he unfolded and tied to the pole to form a square flag a little less than four meters on a side. With the flagpole in hand, he walked along the outside of the dome until he was three or four meters from the edge of the opening. Ariel followed him.

They were walking along the edge of a deep, shimmering hemispherical pit two kilometers across and a kilometer deep. From that viewpoint there was no evidence of the city that they knew existed inside the shimmer.

“Under no circumstances let any part of your body touch or project into the transparent dome,” Wohler-9 said. “That part of you would go through and never be the same again. Now observe the flag.”

He pushed the flag through the dome's glimmer. It seemed to disappear.

“Perhaps it appears to be gone,” he said, waving the pole, “but look carefully at the far side of the pit.”

At first Ariel could see nothing unusual on the other side, but after a moment, after looking more carefully, she finally saw a tiny white flag waving, far away, two kilometers away, on the other side of the pit.

Wohler-9 laid down the pole so that it still projected into the dome. It did not lie flat on the ground. The near end hung suspended, slanting into the dome at the ground. The tiny flag on the other side of the pit had disappeared into the grass.