Even though his head was braced at an odd angle, in preparation for any sudden moves by the captives sitting in front of him, Roger could still see out through the walkers forward windows. In his peripheral field, he watched a lozenge-shaped passenger pod rise smoothly from the hidden gap between the perimeter wall and the gray side of the fountain itself. In two clicks the pod was above the top edge of the windows and gone from sight, on its way to the upper atmosphere. He would have told the grid that the walker was nearly aligned on one of the tower tracks, maybe even the right one—if he could have told the grid anything.
The walker ignored the rising pod and kept poking at the wall.
"What's happening?" Demeter whispered to Mitsuno. "Is he lost or something?"
"I don't know." The hydrologist sounded worried.
Roger himself had to keep mute.
If he could have answered, he might have explained that while most of the cargo riding up and down the fountain went in sealed pods, the builders had provided accommodation for containerized freight and pieces of machinery that were larger and heavier than the standard elevator car. In such cases, the goods were flat-loaded onto a gyro-stabilized platform, anchored against slippage, and sent naked into the vacuum. The grid now wanted to put the walker on such a cargo stage, but first it had to find the entry point into the surf ace loading bay.
And it was doing that by the process of trial and error, which grated intolerably on Roger's human-originated and efficiency-minded sensibilities. If only the grid would release him, let him guide the walker manually—but this was too much trust for the machines to show, even to him.
Ever since his encounter with Dorrie out at Harmo-nia Mundi, Rogers systems had been acting strangely, moving him of their own volition. He was like a marionette being jerked around on its strings. That sensation had horrified him, especially when against his wall he had manhandled Lole Mitsuno—whom Roger actually liked as an honest technician, though a human—and then herded him and Demeter Coghlan up the ramp and into the walker. Torraway knew the grid was using him, accessing his muscles and senses through an override on his backpack interface. It was the same override that let Dorrie appear to Roger and guide him when a consensus of the three cybers governing his sensorium observed or analyzed a potential danger. Now the grid had gotten into his systems through that same keyhole. Roger was hopping mad about it but helpless to change anything.
At last the walker found the fencepost with the right scent. Roger would have laughed, if he could. The access point was a steel door, painted gray like the rest of the concrete wall or the towers superstructure, but outlined with bold yellow-and-black stripes. Any human or Cyborg eye would have spotted the warning border from a couple of hundred meters away. But the grid was using the walkers other sensors—its radio receiver, probably—to search for something more sub-de and meaningful to a machine intelligence, like the magnetic anomaly of the steel panel or the hum of its servomotors.
The grid unlocked the tower door from the inside. The bolts made a clang that Torraway could feel distantly through the walkers deck. The door split and swung outward. As soon as there was clearance for the vehicle's extended pads, it ambled forward into the darkness.
"Where are we going?" Demeter asked aloud. "Lole, you know, don't you?"
"I think we're going to find out firsthand what the grid did with that cargo of explosives," Mitsuno answered.
"Are we hostages?'
"Looks like it."
The walker advanced through a gray twilight, illuminated partly by the glimmer of dawn that came off the desert outside the still-open doors, partly by the star-shine that filtered down from the gap around the base of the fountain structure. Roger wished he could move, if only to press himself up against the walker's windshield and look down ahead of those plodding feet. The grid would assume that the cargo platform was now aligned with this level in this bay because it had issued orders to that effect and received no subsequent error messages. That didn't mean the elevator stage was necessarily in place.
If the walker was going to step off into empty space, tumbling Roger and his friends sixty meters into the fountain's maintenance subbasement, he wanted to be the first to know about it. Maybe he could brace Demeter and Lole somehow, keep them from breaking their necks. But of course he was frozen in his crouch, powerless to intercede.
The timbre of the walker's footsteps changed. The thud of spring-steel pads on dull concrete became the boom of those same hardpoints against huge metallic plates. They were on the platform.
Pushing its nose to within a meter of the tower wall, its front end just fitting between the two tracks of the mass driver, the walker used every centimeter of the lift's available space. Roger could feel it shifting backward and forward, making microadjustments in the placement of its pads for clearance. The grid was cutting its tolerances extremely fine today.
When the machine was finally in position, it dropped a full three meters. Demeter let out a little squeak of fright. But Torraway knew it was simply moving into a more stable crouch on the platform, much like his own posture. As soon as the fuselage stopped rocking on its suspension, dogs around the perimeter of the deck clamped onto the pads and uprights, anchoring the vehicle in place.
"Lole . . ." Demeter began, and Roger could read the dread in her voice. "Is the hull of this thing sealed against vacuum ?"
"Well. .." Mitsuno stopped to think. "Nearly so. I mean, Mars s atmospheric pressure at ground level is about one percent of Earth's. That's close enough to vacuum it makes no difference."
"Uh-huh." She didn't sound convinced. "I guess I have to accept that. You're breathing this air, too."
While she spoke, the side of the tower began to slip down past their window. The wall's surface was so plain and featureless that after that first blur of motion it virtually disappeared, becoming useless as a measure of their upward speed. The press of added weight from the acceleration soon faded out, too. Roger had to push the readouts from strain gauges built into his knees and legs in order sense their rate of climb: now meters per second, building smoothly toward kilometers per second.
As they rose, Torraway felt a strange thing happen: the iron hand that had compelled his movements over the past hour seemed to be releasing him. The connection with the grid was fading. He wondered what could be causing it. Not the grid itself, because it was accustomed to using him casually, like any daughter cyber which had been subordinated to the program hierarchy. Neither reason nor compassion would inspire the grid to let him go. Thus, something was taking him out from under its control.
Of course, the interruption would not arise out of sheer distance as the platform moved away from the nexus buried in Tharsis Montes. The grid's span of control, extended by packet radio repeaters, extended over the breadth of Mars and, with fiberoptic junctions, up the full height of the fountain to oversee all its operations. The nexus administered the satellites in their separate orbits as well.
Then Roger remembered that the fountain was supported by the inertia of thousands, or perhaps millions, of ferrite hoops that were shot aloft at great speed. Their passage would create a powerful magnetic field. And so would the mass drivers that pulled and pushed the cargo pods and this platform along the exterior rails. The conflicting fields would block radio signals into Torraway's backpack computer.