I couldn ’ t either. Something has happened to them.

Then I will gather what robots I can find and come myself.

Make sure Ariel and Wolruf are safe first.

Of course.

Derec felt himself blush. He hadn’t had to order him to do that.

Do you know what happened?he sent.

It appears a newly constructed building has fallen over.

Derec repeated his news for Avery, who had moved back to the lab bench and was fumbling around in a drawer for something.

“Certainly sounded like it,” Avery replied.

Derec shifted his weight from leg to leg. Crouching down was hard to do for more than a minute or so. “But how could a building have fallen over?” he asked.

“Easy. Just shut off the power to it when it’s at an unbalanced stage in its growth. The cells lose their mobility, and the building acts like a solid construction. If it isn’t stable, over it goes. But don’t ask me how the power could get shut off; there’s an entire supervisory subsection devoted to power distribution. Ah, here we go. Where are you?”

“Right here,” Derec said. He reached toward the place where Avery’s voice had come from, encountered his back.

“Shield your eyes.”

Derec just had time to raise his hand over his eyes before a brilliant blue light filled the room. He heard a loud hissing crackle from only a few feet in front of Avery, then the light dimmed and the hissing faded. Derec opened his eyes cautiously and saw Avery holding a cutting laser, now turned to low intensity and pointed up at an angle toward the ceiling. Avery played with the focus and the spot of light widened, but it was still painfully bright, and a wisp of smoke drifted away from it if he held it for too long in one place. It was made for cutting, not illumination, but at least it was light.

They surveyed the remains of the lab. The ceiling had indeed come down, stretching rather than crumbling. It met the floor near the door, and they could see the remains of the wall in which the door had stood smashed beneath it. Nothing had shattered; the building material had simply bent and crumpled under the stress. The monochromatic blue laser light made for stark shadows, accentuating the destruction.

“Evidently the core of the building collapsed,” Avery said. “We’ll have to go out through an exterior wall.” He turned the laser’s intensity up to full again and fired it at the wall opposite the door. The ceiling was still at the proper height there; Avery stepped closer until he could stand comfortably and began cutting a ragged rectangle into the wall. The light beam was nearly invisible at first, except where it met the wall, but within seconds it became a solid blue rod lancing through the smoke.

“Don’t breathe that stuff,” Derec cautioned.

“Good idea.” Avery stepped back and continued to cut. He got the sides and the top done, but the panel remained standing, so he cut along the floor as well. At last the section of wall twisted and toppled outward, landing with a clang on the sidewalk outside. Avery turned the laser intensity back down, took a deep breath, and rushed through the hole.

Derec followed. They jogged out into the street-a peculiarly empty street for one that had just suffered a major disaster-breathed deeply in the fresh air, and looked around them.

The entire city was dark. The rain had stopped earlier in the day, but clouds still masked the stars. The only illumination anywhere came from the laser in Avery’s hand. He turned up the intensity again and waved it around like a spotlight, and they saw collapsed buildings all around them. Most, like the hospital, seemed to have fallen inward rather than crumbling and Calling sideways like a more conventional building would. It was evidently an effect of the building material, though whether it was by conscious design or merely accidental Derec didn’t know.

Their apartment, far down the street from the hospital now that the constraint to hold it next door for Ariel’s vigil had been cancelled, was in an area of lesser damage, but even so Derec felt the urge to run down to it. He held himself back. Mandelbrot had said she was all right; he should concentrate his effort on finding out what had happened and preventing it from happening again.

When Avery shined the light down the street in the other direction, the cause of the destruction became evident.

For a moment it had probably been the tallest building in the city. Now it was the longest, what was left of it. The end nearest them had flattened everything in its path, but it had survived the fall relatively intact. It was still rectangular, at least. That part had to be the base. Farther along its length, where it would have been moving faster when it hit, they could see where it had ripped apart on impact, fragmenting. It crossed the street at an angle, so they couldn’t see what had been the top of the building, but they could see what had become of it all the same. Out there the force of impact had been enough to dissolve the intercellular bonds in the building material, spewing it in all directions. In short, it had splashed.

It had taken quite a few other buildings with it. The destruction fanned out in a wedge, with the narrow end of it nearest the building’s base, which had been less than a block from them.

And now that he looked closely, Derec could see something moving along the building’s edge. It was a single robot, walking slowly toward the sheared-off base.

You,Derec sent. Can you hear me?

Yes. Master Derec. is it not?

That ’ s right. What ’ s your designation?

I am Building Maintenance Technician126.

Was that building your responsibility?

It would have been upon completion. I believe it has now become the responsibility of Salvage Engineer34, but I cannot get supervisory confirmation of that.

You can ’ t reach your supervisor?

That is correct. I cannot reach any of the seven supervisors.

Then I order you to assume general supervisory duties until you regain contact. Can you contact Salvage Engineer34?

I can.

Inform him that he is also a supervisor.

Acknowledged.The robot immediately sent the order, then began directing the robots under his guidance in assessing the damage elsewhere in the city.

“I just promoted two robots to supervisor,” Derec said aloud.

“Good. Tell them to make power restoration their first priority.”

Derec relayed the order, then turned around to look back down the street toward their apartment. Avery obediently shined the light that way again.

A light appeared in the street. It bobbed up and down with the regular rhythm of a robot’s stride, and within moments Mandelbrot stood before them, four more robots flanking him. Even though robots could see perfectly well by infrared light, he carried a more conventional flashlight, presumably for the humans he had come to rescue.

“I am glad to see that you escaped uninjured,” he said. “I was growing concerned. There seems to be no organized effort to restore city functions, and I have been unable to contact any of the normal supervisors. They all seem to have abandoned their duties.”

“That’s impossible,” Avery stated flatly. “Their jobs have been programmed into them. They can’t just up and leave!”

“I do not wish to contradict you,” Mandelbrot replied, “but they appear to have done just that.”

“I suspect they had help,” Derec said. “And I bet we all know just who it was.”

Over the comlink, he shouted, Lucius!