"Or chasing their prey," Ruiz said sourly.

"Maybe. I'll have to think about that dent.i.tion. Closest thing on Earth is a parasite-the lamprey. Rasps its way into a fish and sucks the juices."

Jameson looked at the swarm outside and shuddered.

"Sounds unpleasant."

Dmitri looked pleased with himself. "The only difference between a parasite and a predator is the size of the prey. A mosquito's a parasite, a tiger's a predator. When the predator gets too big for its victim, it tends to kill it, that's all. Maybe these creatures' ancestors ate on the run, like Cape hunting dogs."

Hastily, Jameson changed the subject. "Wouldn't the extra limbs just atrophy? Would evolution really displace them so drastically?"

"Sure," Dmitri said. "Happens all the time. It doesn't even have to wait for evolution. Take the asymmetrical sole. Flounders and other flatfish on Earth start life with the usual bilateral symmetry, with an eye on either side, like free-swimming fish. When they get older and decide to lie on one side, the eye on that side moves around to the other side of the head."

Dmitri paused to snap a picture of a Cygnan applying some instrument to the bubble. Perhaps it was taking a picture of him.

"The clincher is those three eyes," he said after a moment. "What's one doing under the jaw? Simple! No jaw! It's just learned to open like one. It started as three eyestalks around a central orifice."

"So the creature's' just a glorified tube?" Ruiz ventured.

"Well... so are we. But yes." He frowned. "I wonder what's so important about the other end, that the Cygnans have to wrap them up like their heads."

"What I'd like to know," Jameson said, "is how they matched orbits with us. And just by eyeballing it, too!"

"And how do they manage without s.p.a.cesuits?" Ruiz asked.

"Maybe a very tough outer cuticle, like nematodes," Dmitri said.

"What are nematodes?"

"Most numerous animal on Earth. Little parasitic roundworms. Every species of higher plant or animal has at least one species of nematode living off it. Human beings have about fifty. Most you never notice.

They can live in vacuum. Some even live in boiling water, in hot springs."

"Where do you get all these nasty, facts?" Ruiz said.

"My specialty was parasitology," Dmitri said with a self-satisfied smirk. "Good training for an exobiologist. You'd be surprised at some of the adaptations-"

"Later," Ruiz said hastily. He turned to Jameson. "Tod my boy, what are we going to do about our visitors? Can we let a delegation of them inside for a talk?"

"Some of us may go outside," Jameson said. "The skipper's talking it over with Captain Hsieh now."

At that moment a mild sensation washed through his body, as if he were on a descending elevator. He'd suddenly lost his one percent of weight. Ruiz noticed it too. He looked up questioningly. Only Dmitri seemed oblivious. He was opening his mouth for another little lecture, his slippers hooked into the fuzzy surface of the deck.

"Drive's off," Jameson said. "That's odd. We still have another couple of hours of braking to do."

"Mister Jameson!" Boyle was bawling his name from the control balcony.

"Excuse me" Jameson said. He circled the nearest guideline loosely with thumb and forefinger and kicked off into the air. He reached the balcony in a great swoop and swung himself over.

Boyle and Hsieh were hunched over a communicator screen, looking worried. Mike Berry's face looked out at them, grimy and lined. In the background a Chinese technician, illegally present in the American section, was going over a computer display with Quentin.

Boyle looked up at Jameson. "Listen to this," he said.

"... reaction just damped out," Berry was saying. "We can't seem to get it started again. There seems to be a strong magnetic field interfering with the shape of the field squeezing the plasma. And it's playing h.e.l.l with the computers. Timing's all out of whack.

Kay Thorwald, looking grim, was pointing through the bulge of the observation port down along the length of the hull.

"Look!" she cried.

Jameson sighted down the shaft. At the far end a dozen. Cygnans were cl.u.s.tered together, engaged in purposeful activity. He could make out some kind of lattice attached to the ship, encircling the hull.

"That's how they did it, Captain," he said.

Kay's hand flew to her throat. "They'll kill us! Don't they know that? If we don't kill our momentum, we won't go into orbit around Callisto. We'll crash into Jupiter!"

"Captain!" Jameson said. "We've got to damage that structure they've attached to the ship. I'm betting that it won't take much to do it. Smash it up with pry bars wherever the thing looks most fragile. Toss the loose parts into s.p.a.ce. By the time they could replace it, Berry would be able to get the drive working. If we could buy a couple of hours that way, we'd have time to get into a stable orbit."

Grogan gestured at the scurrying hordes of six-limbed creatures outside. "We'd have to get past them."

Jameson drew a breath. "From the spinlock to that point on the hull is about half the length of a football field," he said. "If I have a dozen good people running interference for me, I think I can make it."

"I can't risk it, Tod," Boyle said.

"Captain, it's the only way."

Boyle and Hsieh exchanged a glance. "All right," Boyle said at last. "Let's round up some volunteers."

Jameson kissed Maggie good-bye and gathered the volunteers around him. "Let's go."

There was a strangled cry from Kay. "Look, look! What are they doing to the air lock?"

Jameson glanced out the bubble. Down at the hub of the ship, aliens were cl.u.s.tered all over the surface of the concentric cylinders that contained the spinlocks, thick as bees on honeysuckle. They were centering their attention on one of the outside doors.

A Cygnan with an implement that looked, at this distance, like an Easter egg at the end of a shovel handle was tracing the crack where the door was sealed. In its wake, other Cygnans were inserting toothpicks. When the eye adjusted for distance, the toothpicks became perfectly ordinary-looking crowbars. The Cygnans were already leaning on them, two or three feet hooked somehow into the surface of the hull, the remaining two or three hands bearing down on the bar.

"They're prying the d.a.m.n door open!" Boyle howled.

"Let's get going!" Jameson yelled, starting toward the exit. "Caffrey'll need help."

"Stay where you are, Commander," Boyle ordered.

"But-"

"There's no time."

The hatch flew off. It seemed to catch the Cygnans by surprise. They rose off the ship like a swarm of flies being disturbed. One of them appeared to have been injured by the hatch. After a moment they settled. There was a frosty explosion of air glittering against s.p.a.ce, a white cloud growing larger. Alarms were going off all over the board.

Human bodies were floating out there. Jameson counted three.

"Caffrey must have had the inside door open, trying to get outside to stop them in time," Jameson said.

"The whole middle of the shaft between bulkheads'll be open to vacuum."

Kay glanced at her-instruments. "It is."

The Cygnan with the Easter-egg tool slithered into the opening. Its a.s.sistants oozed after it.

Grogan was beside Jameson, clutching the edge of Kay's console with raw knuckles. "Caffrey would've had the spin matched to the shaft, then. The wheel's still safe. It'd be too hairy for them to try to get through the interface while it's grinding around. They'll come through this way first."

He was wrong. There was another explosion of frost, a big one this time. A couple of hapless Cygnans came tumbling out of the lock, squirming round on their broomsticks to get back to the ship.

"Somebody was riding the cage, trying to get up here." Jameson said. "The bulkhead at the end of the spoke must have been open."

"Who was in that section of the wheel?" Boyle asked, his voice tight.

"That was spoke number three," Kay said, reading the board. "Sickbay."

"How many patients did Doc Brough and Dr. Nyi have?"

"Four, I think," Kay said in a shaken voice.

Jameson asked, "What about Berry and his people? And Po Fu-yung's team? Are they still alive?"

"Yes. The engine section was sealed off. But there's only enough air there to last a few hours."

Grogan's big knuckles were working "We can get 'em out in s.p.a.cesuits, a few at a time. Or carry enough air bottles to them to last until they finish their work."

Kiernan was pushing his way through the crowd. "The hydroponics section!" he said. "Did it lose its air?"

Yeh Fei answered him. "Yes. But the no-gravity farm is still alive. The bulkhead forward of the spinlock was sealed."

"Can that keep us going?" Boyle asked.

Kiernan put his head together with Dmitri. After a mumbled exchange, he looked up again. "Yes. If nothing else happens we can get some new algae tanks going. We may have to spread out into the observatory and bridge. And if we can pressurize the ring again, I can reestablish a hydroponics section there with transplants from the banks in no-g. We won't be eating well for a while, but we'll breathe."

"Unless..." Everybody turned to look at Jameson. "Unless they kill off the rest of our greenery before we can stop them."

"All right," Boyle said. "We're under siege. Grogan, we're going to need all the s.p.a.cesuits from the spinlock lockers. And somebody's going to have to go through vacuum to get them. How many suits can we sc.r.a.pe up here in the forward part of the ship?"

"Captain, there's just four. They're in the auxiliary air lock near the observatory. At least they were last time I checked. But we can't send anyone to the spinlock until I jury-rig some kind of air lock south of the no-g farm."

"How long will that take you?"

Grogan thought it over. "I can make it out of a water tank. A couple of hours."

Jameson looked out the window. He could see a general movement of Cygnans toward the breached lock. Frozen air was still misting out into s.p.a.ce.

"Skipper," he said, "we don't have a couple of hours"

Boyle brooded at him from under heavy eyebrows. "No, we don't. Once they get into the ship..."

He didn't need to finish the thought. Everybody there was thinking about what would happen if the Cygnans breached any more bulkheads. The humans were trapped in their own ship, in two fragile bubbles of air at either end of the long shaft that pierced the wheel. Even if they all could get into s.p.a.cesuits-those unreachable suits in the spinlock-it would only prolong their death sentence.

Kiernan bit his lip. "Come on, w.a.n.g," he said. "Let's get down to the farm and get as much seed stock as we can into airtight lockers."

"Do you know how dangerous that is, Mr. Kiernan?" Boyle interrupted. "You'll be one bulkhead closer to vacuum. a.s.suming we can get the ship repressurized, is there really going to be enough time to reestablish an ecology before the reserve air runs out?"

"I don't know," Kiernan admitted. "But we've got to try."

"I'll go with you," Dmitri volunteered abruptly. "You'll need a lot of help. You'd better have a biologist along." The boyish face didn't look weak any more. Dmitri's voice was shaking, but his self-indulgent mouth was set in firm lines now. Jameson had to admire his guts.

"I go too," a harsh voice said. "I am biologist." They looked up. Tu Jue-chen was there, biting her lip.

Her homely face was tight and unreadable.

"Thank you,Tongzhi Tu," Boyle said.

"I'd better get started," Jameson said. "I'll have to try to run the gauntlet with just two men. I'd better leave the fourth s.p.a.cesuit here. Somebody may still be able to make it to the spinlock storage lockers for some more suits if Grogan can rig up that air lock before the Cygnans decide to come inside." He turned to Grogan. "You'd better get cracking, Chief."

"The h.e.l.l I will," Grogan rumbled. "I'm coming with you. One of my boys'll volunteer to rig the lock." He called out over the crowd. "Fiaccone, that's you!"

"Right you are, Chief," Fiaccone said, grinning. He headed toward the exit in a no-gravity shamble.

Yeh Fei rose from his chair, looming over the rest of them. "I am third man," he said. n.o.body argued with him.

Jameson said good-bye to Maggie again, clasping her thin body in his arms. He felt her tremling. "I'll be back," he said, whispering. "Nothing says the Cygnans have to be malicious. Maybe they're just curious."

She was wound around him with all her strength. He broke free gently and turned to Grogan and Yeh.

"All set," he said.

The three of them suited up in the auxiliary lock behind the observatory. Yeh had armed himself with a wicked-looking cargo hook. Grogan had his fist wrapped around the handle of a sixteen-pound sledgehammer, just behind its head. The short handle was forward. He could poke with it, or swing his fist with the heavy lump of metal in it. Jameson had along pry bar.

Just before they spun the outer door open, there was a disconcerting moment when a Cygnan peered in at them through the small safety window. Its three orange pupils expanded from a narrow slit, like an unfolding fan. Then the creature blinked and was gone.

If Dmitri was right, there was no brain behind those three strange eyes. What unimaginable thoughts went on between what pa.s.sed for a Cygnan's shoulders?

"Go!" Jameson commanded.

The hull immediately outside the airlock was a crawling carpet of mottled flesh. A sea of pikes bobbed and waved above it: the Cygnans' flying broomsticks. They held them absent-mindedly, pa.s.sing them from hand to middle limb to foot as they jostled one another to converge on the opening lock. The clever little toes clung to any projection or surface irregularity on the hull.

Jameson scrambled forward, Yeh and Grogan flanking him in a flying wedge. The carpet of alien life opened up ahead of them and closed again behind them. Yeh was swinging his long hook in circles to keep them at a distance. Grogan poked with his sledge handle. Cygnans skipped nimbly out of the way.

My G.o.d, we're going to make it!was Jameson's first thought. But then, before they had gone twenty feet, the Cygnans began closing in.

Yeh made a swipe with his hook and ripped the balloonlike sheath over a Cygnan's long snout. Vapor puffed out into s.p.a.ce; and the Cygnan died. Jameson could see orange blood oozing out of the eyestalks.

Then, before the swing could be completed, Cygnan fingers closed on the shaft of the cargo hook. Yeh shook the grip off with his enormous strength, but the Cygnan simply shifted its grip to a middle limb. A companion came to, help it and easily s.n.a.t.c.hed the hook out of Yeh's grasp; Yeh's weapon pa.s.sed from Cygnan to Cygnan until it was out of sight.