"Precisely," Danchekker affirmed. "Extraordinary."

The mission director glanced at the clock on the dining-room wall, then spread his arms along the edge of the table in a gesture of finality.

"Well, gentlemen," he said. "It's been a pleasure meeting you both at last. Thank you for a most interesting conversation. We must make a point of keeping in touch regularly from now on. I have to attend an appointment shortly, but I haven't forgotten that I promised to show you the ship's command center. So, if you're ready, we'll go there now. I'll introduce you to Captain Hayter who's to show you around. Then, I'm afraid, you'll have to excuse me."

Fifteen minutes later, after riding a capsule through one of the ship's communications tubes to reach another section of the vessel, they were standing surrounded on three sides by a bewildering array of consoles, control stations and monitor panels on the bridge; below them stretched the brilliantly lit panorama of Jupiter Five's command center. The clusters of operator stations, banks of gleaming equipment cubicles and tiers of instrument panels were the nerve center from which ultimately all the activities of the mission and all the functions of the ship were controlled. The permanent laser link that handled the communications traffic to Earth; the data channels to the various surface installations and the dispersed fleet of UNSA ships nosing around the Jovian system; the navigation, propulsion and in-flight control systems; the heating, cooling, lighting, life-support systems and ancillary computers and machinery, and a thousand and one other processes--all were supervised and coordinated from this stupendous concentration of skills and technology.

Captain Ronald Hayter stood behind the two scientists and waited as they took in the scene below the bridge. The mission was organized and its command hierarchy structured in such a way that operations were performed under the ultimate direction of the Civilian Branch of the Space Arm; supreme authority lay with Shannon. Many functions essential to UNSA operations, such as crewing spaceships and conducting activities safely and effectively in unfamiliar alien environments, called for standards of training and discipline that could only be met by a military-style command structure and organization. The Uniformed Branch of the Space Arm had been formed in response to these needs; also, not entirely fortuitously, it went a long way toward satisfying peacefully the longing for adventure of a significant proportion of the younger generation, to whom the idea of large-scale, regular armed forces belonged to a past that was best forgotten. Hayter was in command of all uniformed ranks present aboard J5 and reported directly to Shannon.

"It's quiet at the moment compared to what it can be like," Hayter commented at last, stepping forward to stand between them. "As you can see, a number of sections down there aren't manned; that's because lots of things are shut down or just under automatic supervision while we're parked in orbit. This is just a skeleton crew up here too."

"Seems to be some activity over there," Hunt said. He pointed down at a group of consoles where the operators were busily scanning viewscreens, tapping intermittently into keyboards and speaking into microphones and among themselves. "What's going on?"

Hayter followed his finger, then nodded. "We're hooked into a cruiser that's been in orbit over Io for a while now. They've been putting a series of probes in low-altitude orbits over Jupiter itself and the next phase calls for surface landings. The probes are being prepared over Io right now and the operation will be controlled from the ship there. The guys you're looking at are simply monitoring the preparation." The captain indicated another section further over to the right. "That's traffic control. . . keeping tabs on all the ship movements around the various moons and in between. They're always busy."

Danchekker had been peering out over the command center in silence. At last he turned toward Hayter with an expression of undisguised wonder on his face.

"I must say that I am very impressed," he said. "Very impressed indeed. On several occasions during our outward voyage, I'm afraid that I referred to your ship as an infernal contraption; it appears that I am now obliged to eat my words."

"Call it what you like, Professor," Hayter replied with a grin. "But it's probably the safest contraption ever built. All the vital functions that are controlled from here are fully duplicated in an emergency command center located in a completely different part of the ship. If anything wiped out this place, we could still get you home okay. If something happened on a large enough scale to knock out both of them--well . . ." he shrugged, "I guess there wouldn't be much of the ship left to get home anyhow."

"Fascinating," Danchekker mused. "But tell me--"

"Excuse me, sir." The watch officer interrupted from his station a few feet behind them. Hayter turned toward him.

"What is it, Lieutenant?"

"I have the radar officer on the screen. Unidentified object detected by long-range surveillance. Approaching fast."

"Activate the second officer's station and switch it through. I'll take it there."

"Aye aye, sir."

"Excuse me," Hayter muttered. He moved over to the empty seat in front of one of the consoles, sat down and flipped its main screen into life. Hunt and Danchekker took a few paces to bring them a short distance behind him. Over his shoulder they could see the features of the ship's radar officer materialize.

"Something unusual going on, Captain," he said. "Unidentified object closing on Ganymede. Range eighty-two thousand miles; speed fifty miles per second but reducing; bearing two-seven-eight by oh-one-six solar. On a direct-approach course. ETA computed at just over thirty minutes. Strong echoes at quality seven. Reading checked and confirmed."

Hayter stared back at him for a second. "Do we have any ships scheduled in that sector?"

"Negative, sir."

"Any deviations from scheduled flight plans?"

"Negative. All ships checked and accounted for."

"Trajectory profile?"

"Inadequate data. Being monitored."

Hayter thought for a moment. "Stay live and continue reporting." Then he turned to the watch officer: "Call the duty bridge crew to stations. Locate the mission director and alert him to stand by for a call to the bridge."

"Yes, sir."

"Radar." Hayter directed his gaze back at the screen on the panel in front of him. "Slave optical scanners to LRS. Track on UFO bearing and copy onto screen three, J5. " Hayter paused for a second, then addressed the watch officer again. "Alert traffic control. All launches deferred until further notice. Arrivals scheduled at J5 within the next sixty minutes are to stand off and await instructions."

"Do you want us to leave?" Hunt asked quietly. Hayter glanced around at him.

"No, that's okay," he said. "Stick around. Maybe you'll see some action."

"What is it?" Danchekker asked.

"I don't know." Hayter's face was serious. "We've never had anything like this before."

Tension rose as the minutes ticked by. The duty crew appeared quickly in ones and twos and took up their positions at the consoles and panels on the bridge. The atmosphere was quiet but charged with suspense as the well-oiled machine readied itself. . . and waited.

The telescopic image resolved by the optical scanners was distinct, but impossible to interpret: circular overall, it appeared to possess four thin protuberances in cruciform, with one pair somewhat long and slightly thicker than the other. It could have been a disk, or a spheroid, or perhaps it was something else seen end-on. There was no way of telling.

Then the first view came in via the laser link to Jupiter Four , orbiting Callisto. Because of the relative positions of Ganymede and Callisto, and of the rapidly diminishing range of the intruder, the telescopes on the Jupiter Four obtained an oblique view from a position some distance from its projected course, to Ganymede.