Ariel hesitated while the function robot placed the small box inside the capsule between her feet and Derec’s head. She squatted down quickly and stretched out just as the function robot closed the trapdoor.

“We’re going wherever this box is,” she said. “The good thing is, we haven’t left any kind of trail. That programming is completely independent of us. “

“Yeah-”

His comment was cut short by the sudden acceleration of the capsule. It moved forward on rollers to push through a door that gave under the pressure. Then they were in the vacuum tube itself, and the capsule really picked up speed.

As before, the momentum pushed both of them back against the rear of the capsule. Derec was too sore to brace himself with his arms, so his head and shoulder were jammed against the back surface. They were rushing through darkness, blasted by the air that swept over them from unseen vents.

Before, the flight from their pursuers had kept his adrenaline flowing, and he had experienced some remission of his stiffness. Now even the excitement of riding the vacuum tube was not enough to keep the symptoms from recurring. His legs continued to throb painfully, and the shooting pains in his back seemed to settle in with the increasing stiffness he felt.

His one relief was that she was right. They had not left a trail.

The tube curved upward. He closed his eyes in anticipation of light, and brilliant sunlight flooded the capsule. Opening his eyes slowly so they could adjust, he took in the new scene around them.

This section of the transparent vacuum tube rose high above the ground and used the existing supports of various buildings to wind over the city. At this altitude-and it was still rising-it would not interfere with earthbound priorities. Their capsule was shooting along the tube at high speed over what should have been a spectacular view. He was in too much pain to enjoy it.

Suddenly a thought struck him.

“Ariel,” he said, with effort. “That entire staff at the Key Center has been reassigned. But it was the Key Center that provided the vacuum to run this vacuum tube system. That means the Key Center itself is still working. What’s going on around here, anyway?”

She didn’t answer.

“Ariel?” He called louder over the rushing air, but he knew what her silence meant. With a sinking feeling, he turned his head to look at her, feeling more snappings in his neck.

She lay on her back, holding herself in position by pushing against the rear of the capsule with both hands. Her face, turned to the side, showed exhilaration and excitement as she gazed at the panorama of the city. She did not seem to see him at all.

Derec guessed that she was reliving their first wild ride in the vacuum tube, long ago. It was a happier period in some ways, though they had felt burdens at the time. At least he had been healthy, and she had been functionally so before her disease had really struck.

He turned his face away from her. If she was reexperiencing those memories, she was probably more comfortable at the moment. He could let her have that. Then, once they were safely out of this capsule, they could get their bearings.

The tube did not always go straight. Its various straightaways were broken with curves, loops, and changes in altitude. These most often simply accommodated architecture that must have been already in place. Sometimes they brought the capsule to an intersection of tubes, where curves allowed it to change direction with minimal loss of speed. Occasionally the shifts in direction led by depot sidings that their capsule shot past. Every so often the tunnel dipped underground, and once it ran along the ceiling of the platform booth tunnel system for an extended period.

Finally the capsule leveled off near the ground and decelerated sharply into a siding. It stopped abruptly, sliding them both to the front of the tube with the small package. Derec lay panting on his back, looking up through the transparent capsule and tube at the impassive face of a Hunter robot.

The slidewalk was the slowest of Robot City’s powered transportation systems. Mandelbrot and Wolruf followed the single Hunter on it with increasing boldness. The various Hunters had obviously taken different assignments and they had no way of knowing what role this Hunter actually had.

“Not too close,” hissed Wolruf softly over Mandelbrot’s shoulder. “ ‘U will get itss attention, I tell ‘u.”

“I doubt it,” said Mandelbrot. “I now think it, as a Hunter, maintains an awareness of everything around it. It must have scanned us and rejected us as its quarry.”

“That iss sstupid,” said Wolruf.

“Eh?” Mandelbrot said stiffly.

“Not ‘u. ‘Im,” she said patiently. “Why would theirr order include Derec and Ariel but not us?”

“It does seem to be poor programming,” said Mandelbrot. “However, I do not judge it as stupidity.”

“Then what?”

Up ahead, the Hunter still advanced along the moving slidewalk. It seemed to know where it was going.

“Derec often spoke of the single-rnindedness of Avery robots,” Mandelbrot explained. “Their task orientation is narrow. If the central computer or the Supervisors, or even Avery himself, learned of the presence of Derec and Ariel, perhaps the order to the Hunters specifically named them and did not extend to anyone else.”

Wolruf shook her head at the Hunter ahead of them. “Iss stupid. Good for us, but still stupid.”

Ahead of them, the Hunter moved on. Mandelbrot strode tirelessly after it.

Derec and Ariel were in no shape to protest as two Hunter robots lifted them out of the capsule door. The function robot on the dock waited until the humans were out before grabbing the small package that had been scheduled for the trip. Derec hurt allover and was simply too weak to struggle.

One Hunter held him by the arm, and he actually leaned against the robot for support. Ariel was just now blinking at the Hunter holding her. He recognized that as one of the signs that she was coming back out of her latest memory fugue.

“Ariel,” he said quietly.

She turned at the sound of his voice, then started at the sight of the Hunters. “Derec-”

“They’ve got us,” he muttered wearily. He shook his head as the Hunters turned and started for the nearest slidewalk, pulling them along in their inflexible grips.

Derec still tried to think of a way out of this. They were positronic robots and would respond to protests based on the Laws. From past experience, however, he also knew that they had been programmed to detain and arrest humans without harming them. He could argue, but he didn’t know how to win.

Besides, he was just too tired. Derec stumbled several times, forcing himself to keep up with the Hunter. Finally the Hunter lifted him bodily and carried him, not out of concern but for efficiency of travel. The other Hunter lifted Ariel at the same time.

The Hunters turned to ride the slidewalks and Derec found himself facing Ariel.

“How did they get us?” She mouthed the words silently, with a quick glance at her captor’s head.

“I don’t think they care if we talk,” he said aloud. “I’m guessing now that some other Hunters started by questioning the tunnel-system computer. That gave them the coordinates of the tunnel stop where we got off the platform booth, as I was afraid might happen. From there they must have used heat sensors to track us along the street to the vacuum tube depot.”

“But the capsule in the vacuum tube goes so fast. How did they get in front of us?”

“They must have found out which depot that package was going to and called ahead to have these guys waiting for us.”

“After that long ride,” said Ariel. “You make catching us sound so simple.”

“Apparently it was,” he said ruefully.

“They’ve got us,” she said, in a voice that cracked. “Derec, look out! They’re right behind us in the conduit-”