The image on the screen tilted and swooped dizzily as the skyball skidded and slid across the sky. It was having trouble navigating in the wind. After a moment, though, it figured out what it was doing and the image steadied into a long glide...

I nodded and tapped at the keyboard, bringing the drone lower. The image turned slowly as the skyball circled the nest. I punched for scanning. The image shifted colors then: blue for cold, red for hot, yellow for in between. Most of the screen was orange. I had to turn down the range.

The corrected scan was mostly green and yellow. A faint orange track led to the dome. Or away from it. The track was at least an hour old.

I glanced at Duke; his expression was unreadable. "Scan the dome," he said.

We knew that the worms were hot when they were active. But we also knew that when they went torpid-which was usually during the hottest part of the day-their body temperatures could drop as much as thirty degrees. That was why the earliest mobile probes had failed to register their presence. The worms had been too cool.

We knew better now.

The worms went deep and they went cold. Men had died to find that out.

The skyball came in low and close now. The dome filled the screen. I punched in a sonic-scan overlay. There was something there, all right-a dark blue mass, mottled with quickly shifting colors. It was large and deep below the surface.

The screen said it massed four tons.

"That's a good-sized family," said Duke. "Can we take 'em?" 

I was wondering the same thing, "Denver says the gas is good. This is at the upper end of the range, but it's within the limit." 

"How do you feel about it?"

"I say go."

"Good," said Duke. "So do I." He thumbed his mike. "All units. It's a go. I repeat, it is a go. Proceed to your final positions. This is it."

We were committed now. There were no more Go-NoGo points. Duke leaned forward and rapped our driver. "Come on-let's move!" The big rollagon trundled forward, up a small ridge and then down the long slope on the opposite side.