It was a virus, beyond doubt. The electron microscope told them that, now that they had the substance isolated and could examine it. In the culture tubes in the Lancet's incubators, it would begin to grow nicely, and then falter and die, but when guinea pigs were inoculated in the ship's laboratory, the substance proved its virulence. The animals injected with tiny bits of the substance grew sick within hours and very quickly died.

The call to the Hospital Ship was canceled as the three doctors worked in feverish excitement. Here at last was something they could grapple with, something so common among the races of the galaxy that the doctors felt certain that they could cope with it. Very few, if any, higher life forms existed that did not have some sort of submicroscopic parasite afflicting them. Bacterial infection was a threat on every inhabited world, and the viruses—the tiniest of all submicroscopic organisms—were the most difficult and dangerous of them all.

And yet virus plagues had been stopped before, and they could be stopped again.

Jack radioed down to the planet's surface that the diagnosis had been made; as soon as the proper medications could be prepared, the doctors would land to begin treatment. There was a new flicker of hopefulness in the Bruckian's response, and an appeal to hurry. With renewed energy the doctors went back to the lab to start working on the new data.

But trouble continued to dog them. This was no ordinary virus. It proved resistant to every one of the antibiotics and antiviral agents in the Lancet's stockroom. No drug seemed to affect it, and its molecular structure was different from any virus that had ever been recorded before.

"If one of the drugs would only just slow it up a little, we'd be ahead," Tiger said in perplexity. "We don't have anything that even touches it, not even the purified globulins."

"What about antibodies from the infected people?" Jack suggested. "In every virus disease I've ever heard of, the victim's own body starts making antibodies against the invading virus. If enough antibodies are made fast enough, the virus dies and the patient is immune from then on."

"Well, these people don't seem to be making any antibodies at all," Tiger said. "At least not as far as I can see. If they were, at least some of them would be recovering from the disease. So far not a single one has recovered once the thing started. They all just go ahead and die."

"I wonder," Dal said, "if Fuzzy had any defense."

Jack looked up. "How do you mean?"

"Well, Fuzzy was infected, we know that. He might have died too, if we hadn't caught it in time—but as it worked out, he didn't. In fact, he looks pretty healthy right now."

"That's fine for Fuzzy," Jack said impatiently, "but I don't see how we can push the whole population of 31 Brucker VII through a virus filter. They're flesh-and-blood creatures."

"That's not what I mean," Dal said. "Maybe Fuzzy's body developed antibodies against the virus while he was infected. Remember, he doesn't have a rigid body structure like we do. He's mostly just basic protein, and he can synthesize pretty much anything he wants to or needs to."

Jack blinked. "It's an idea, at least. Is there any way we can get some of his body fluid away from him? Without getting bit, I mean?"

"No problem there," Dal said. "He can regenerate pretty fast if he has enough of the right kind of food. He won't miss an ounce or two of excess tissue."

He took a beaker over to Fuzzy's platform and began squeezing off a little blob of pink material. Fuzzy seemed to sense what Dal wanted; obligingly he thrust out a little pseudopod which Dal pinched off into the beaker. With the addition of a small amount of saline solution, the tissue dissolved into thin, pink suspension.

In the laboratory they found two or three of the guinea pigs in the last stages of the infection, and injected them with a tiny bit of the pink solution. The effect was almost unbelievable. Within twenty minutes all of the injected animals began to perk up, their eyes brighter, nibbling at the food in their cages, while the ones that had not been injected got sicker and sicker.

"Well, there's our answer," Jack said eagerly. "If we can get some of this stuff injected into our friends down below, we may be able to protect the healthy ones from getting the plague, and cure the sick ones as well. If we still have enough time, that is."

They had landing permission from the Bruckian spokesman within minutes, and an hour later the Lancet made an orderly landing on a newly-repaved landing field near one of the central cities on the seventh planet of 31 Brucker.

Tiger and Jack had obviously not exaggerated the strange appearance of the towns and cities on this plague-ridden planet, and Dal was appalled at the ravages of the disease that they had come to fight. Only one out of ten of the Bruckians was still uninfected, and another three out of the ten were clearly in the late stages of the disease, walking about blankly and blindly, stumbling into things in their paths, falling to the ground and lying mute and helpless until death came to release them. Under the glaring red sun, weary parties of stretcher bearers went about the silent streets, moving their grim cargo out to the mass graves at the edge of the city.

The original spokesman who had come up to the Lancet was dead, but another had taken his place as negotiator with the doctors—an older, thinner Bruckian who looked as if he carried the total burden of his people on his shoulders. He greeted them eagerly at the landing field. "You have found a solution!" he cried. "You have found a way to turn the tide—but hurry! Every moment now is precious."

During the landing procedures, Dal had worked to prepare enough of the precious antibody suspension, with Fuzzy's co-operation, to handle a large number of inoculations. By the time the ship touched down he had a dozen flasks and several hundred syringes ready. Hundreds of the unafflicted people were crowding around the ship, staring in open wonder as Dal, Jack and Tiger came down the ladder and went into close conference with the spokesman.

It took some time to explain to the spokesman why they could not begin then and there with the mass inoculations against the plague. First, they needed test cases, in order to make certain that what they thought would work in theory actually produced the desired results. Controls were needed, to be certain that the antibody suspension alone was bringing about the changes seen and not something else. At last, orders went out from the spokesman. Two hundred uninfected Bruckians were admitted to a large roped-off area near the ship, and another two hundred in late stages of the disease were led stumbling into another closed area. Preliminary skin-tests of the antibody suspension showed no sign of untoward reaction. Dal began filling syringes while Tiger and Jack started inoculating the two groups.

"If it works with these cases, it will be simple to immunize the whole population," Tiger said. "From the amounts we used on the guinea pigs, it looks as if only tiny amounts are needed. We may even be able to train the Bruckians to give the injections themselves."

"And if it works we ought to have a brand new medical service contract ready for signature with Hospital Earth," Jack added eagerly. "It won't be long before we have those Stars, you wait and see! If we can only get this done fast enough."

They worked feverishly, particularly with the group of terminal cases. Many were dying even as the shots were being given, while the first symptoms of the disease were appearing in some of the unafflicted ones. Swiftly Tiger and Jack went from patient to patient while Dal kept check of the names, numbers and locations of those that were inoculated.

And even before they were finished with the inoculations, it was apparent that they were taking effect. Not one of the infected patients died after inoculation was completed. The series took three hours, and by the time the four hundred doses were administered, one thing seemed certain: that the antibody was checking the deadly march of the disease in some way.

The Bruckian spokesman was so excited he could hardly contain himself; he wanted to start bringing in the rest of the population at once. "We've almost exhausted this first batch of the material," Dal told him. "We will have to prepare more—but we will waste time trying to move a whole planet's population here. Get a dozen aircraft ready, and a dozen healthy, intelligent workers to help us. We can show them how to use the material, and let them go out to the other population centers all at once."

Back aboard the ship they started preparing a larger quantity of the antibody suspension. Fuzzy had regenerated back to normal weight again, and much to Dal's delight had been splitting off small segments of pink protoplasm in a circle all around him, as though anticipating further demands on his resources. A quick test-run showed that the antibody was also being regenerated. Fuzzy was voraciously hungry, but the material in the second batch was still as powerful as in the first.

The doctors were almost ready to go back down, loaded with enough inoculum and syringes to equip themselves and a dozen field workers when Jack suddenly stopped what he was doing and cocked an ear toward the entrance lock.

"What's wrong?" Dal said.

"Listen a minute."

They stopped to listen. "I don't hear anything," Tiger said.

Jack nodded. "I know. That's what I mean. They were hollering their heads off when we came back aboard. Why so quiet now?"

He crossed over to the viewscreen scanning the field below, and flipped on the switch. For a moment he just stared. Then he said: "Come here a minute. I don't like the looks of this at all."

Dal and Tiger crowded up to the screen. "What's the matter?" Tiger said. "I don't see ... wait a minute!"

"Yes, you'd better look again," Jack said. "What do you think, Dal?"

"We'd better get down there fast," Dal said, "and see what's going on. It looks to me like we've got a tiger by the tail...."

They climbed down the ladder once again, with the antibody flasks and sterile syringes strapped to their backs. But this time the greeting was different from before.

The Bruckian spokesman and the others who had not yet been inoculated drew back from them in terror as they stepped to the ground. Before, the people on the field had crowded in eagerly around the ship; now they were standing in silent groups staring at the doctors fearfully and muttering among themselves.

But the doctors could see only the inoculated people in the two roped-off areas. Off to the right among the infected Bruckians who had received the antibody there were no new dead—but there was no change for the better, either. The sick creatures drifted about aimlessly, milling like animals in a cage, their faces blank, their jaws slack, hands wandering foolishly. Not one of them had begun reacting normally, not one showed any sign of recognition or recovery.

But the real horror was on the other side of the field. Here were the healthy ones, the uninfected ones who had received preventative inoculations. A few hours before they had been left standing in quiet, happy groups, talking among themselves, laughing and joking....

But now they weren't talking any more. They stared across at the doctors with slack faces and dazed eyes, their feet shuffling aimlessly in the dust. All were alive, but only half-alive. The intelligence and alertness were gone from their faces; they were like the empty shells of the creatures they had been a few hours before, indistinguishable from the infected creatures in the other compound.

Jack turned to the Bruckian spokesman in alarm. "What's happened here?" he asked. "What's become of the ones we inoculated? Where have you taken them?"

The spokesman shrank back as though afraid Jack might reach out to touch him. "Taken them!" he cried. "We have moved none of them! Those are the ones you poisoned with your needles. What have you done to make them like this?"

"It—it must be some sort of temporary reaction to the injection," Jack faltered. "There was nothing that we used that could possibly have given them the disease, we only used a substance to help them fight it off."

The Bruckian was shaking his fist angrily. "It's no reaction, it is the plague itself! What kind of evil are you doing? You came here to help us, and instead you bring us more misery. Do we not have enough of that to please you?"

Swiftly the doctors began examining the patients in both enclosures, and on each side they found the same picture. One by one they checked the ones that had previously been untouched by the plague, and found only the sagging jaws and idiot stares.

"There's no sense examining every one," Tiger said finally. "They're all the same, every one."

"But this is impossible," Jack said, glancing apprehensively at the growing mob of angry Bruckians outside the stockades. "What could have happened? What have we done?"

"I don't know," Tiger said. "But whatever we've done has turned into a boomerang. We knew that the antibody might not work, and the disease might just go right ahead, but we didn't anticipate anything like this."

"Maybe some foreign protein got into the batch," Dal said.

Tiger shook his head. "It wouldn't behave like this. And we were careful getting it ready. All we've done was inject an antibody against a specific virus. All it could have done was to kill the virus, but these people act as though they're infected now."

"But they're not dying," Dal said. "And the sick ones we injected stopped dying, too."

"So what do we do now?" Jack said.

"Get one of these that changed like this aboard ship and go over him with a fine-toothed comb. We've got to find out what's happened."

He led one of the stricken Bruckians by the hand like a mindless dummy across the field toward the little group where the spokesman and his party stood. The crowd on the field were moving in closer; an angry cry went up when Dal touched the sick creature.

"You'll have to keep this crowd under control," Dal said to the spokesman. "We're going to take this one aboard the ship and examine him to see what this reaction could be, but this mob is beginning to sound dangerous."

"They're afraid," the spokesman said. "They want to know what you've done to them, what this new curse is that you bring in your syringes."

"It's not a curse, but something has gone wrong. We need to learn what, in order to deal with it."

"The people are afraid and angry," the spokesman said. "I don't know how long I can control them."

And indeed, the attitude of the crowd around the ship was very strange. They were not just fearful; they were terrified. As the doctors walked back to the ship leading the stricken Bruckian behind them, the people shrank back with dreadful cries, holding up their hands as if to ward off some monstrous evil. Before, in the worst throes of the plague, there had been no sign of this kind of reaction. The people had seemed apathetic and miserable, resigned hopelessly to their fate, but now they were reacting in abject terror. It almost seemed that they were more afraid of these walking shells of their former selves than they were of the disease itself.

But as the doctors started up the ladder toward the entrance lock the crowd surged in toward them with fists raised in anger. "We'd better get help, and fast," Jack said as he slammed the entrance lock closed behind them. "I don't like the looks of this a bit. Dal, we'd better see what we can learn from this poor creature here."

As Tiger headed for the earphones, Dal and Jack went to work once again, checking the blood and other body fluids from the stricken Bruckian. But now, incredibly, the results of their tests were quite different from those they had obtained before. The blood sugar and protein determinations fell into the pattern they had originally expected for a creature of this type. Even more surprising, the level of the antibody against the plague virus was high—far higher than it could have been from the tiny amount that was injected into the creature.

"They must have been making it themselves," Dal said, "and our inoculation was just the straw that broke the camel's back. All of those people must have been on the brink of symptoms of the infection, and all we did was add to the natural defenses they were already making."

"Then why did the symptoms appear?" Jack said. "If that's true, we should have been helping them, and look at them now!"

Tiger appeared at the door, scowling. "We've got real trouble, now," he said. "I can't get through to a hospital ship. In fact, I can't get a message out at all. These people are jamming our radios."

"But why?" Dal said.

"I don't know, but take a look outside there."

Through the viewscreen it seemed as though the whole field around the ship had filled up with the crowd. The first reaction of terror now seemed to have given way to blind fury; the people were shouting angrily, waving their clenched fists at the ship as the spokesman tried to hold them back.

Then there was a resounding crash from somewhere below, and the ship lurched, throwing the doctors to the floor. They staggered to their feet as another blow jolted the ship, and another.

"Let's get a screen up," Tiger shouted. "Jack, get the engines going. They're trying to board us, and I don't think it'll be much fun if they ever break in."

In the control room they threw the switches that activated a powerful protective energy screen around the ship. It was a device that was carried by all GPP Ships as a means of protection against physical attack. When activated, an energy screen was virtually impregnable, but it could only be used briefly; the power it required placed an enormous drain on a ship's energy resources, and a year's nuclear fuel could be consumed in a few hours.

Now the screen served its purpose. The ship steadied, still vibrating from the last assault, and the noise from below ceased abruptly. But when Jack threw the switches to start the engines, nothing happened at all.

"Look at that!" he cried, staring at the motionless dials. "They're jamming our electrical system somehow. I can't get any turn-over."

"Try it again," Tiger said. "We've got to get out of here. If they break in, we're done for."

"They can't break through the screen," Dal said.

"Not as long as it lasts. But we can't keep it up indefinitely."

Once again they tried the radio equipment. There was no response but the harsh static of the jamming signal from the ground below. "It's no good," Tiger said finally. "We're stuck here, and we can't even call for help. You'd think if they were so scared of us they'd be glad to see us go."

"I think there's more to it than that," Dal said thoughtfully. "This whole business has been crazy from the start. This just fits in with all the rest." He picked Fuzzy off his perch and set him on his shoulder as if to protect him from some unsuspected threat. "Maybe they're afraid of us, I don't know. But I think they're afraid of something else a whole lot worse."

There was nothing to be done but wait and stare hopelessly at the mass of notes and records that they had collected on the people of 31 Brucker VII and the plague that afflicted them.

Until now, the Lancet's crew had been too busy to stop and piece the data together, to try to see the picture as a whole. But now there was ample time, and the realization of what had been happening here began to dawn on them.

They had followed the well-established principles step by step in studying these incredible people, and nothing had come out as it should. In theory, the steps they had taken should have yielded the answer. They had come to a planet where an entire population was threatened with a dreadful disease. They had identified the disease, found and isolated the virus that caused it, and then developed an antibody that effectively destroyed the virus—in the laboratory. But when they had tried to apply the antibody in the afflicted patients, the response had been totally unexpected. They had stopped the march of death among those they had inoculated, and had produced instead a condition that the people seemed to dread far more than death.

"Let's face it," Dal said, "we bungled it somehow. We should have had help here right from the start. I don't know where we went wrong, but we've done something."

"Well, it wasn't your fault," Jack said gloomily. "If we had the right diagnosis, this wouldn't have happened. And I still can't see the diagnosis. All I've been able to come up with is a nice mess."

"We're missing something, that's all," Dal said. "The information is all here. We just aren't reading it right, somehow. Somewhere in here is a key to the whole thing, and we just can't see it."

They went back to the data again, going through it step by step. This was Jack Alvarez's specialty—the technique of diagnosis, the ability to take all the available information about a race and about its illness and piece it together into a pattern that made sense. Dal could see that Jack was now bitterly angry with himself, yet at every turn he seemed to strike another obstacle—some fact that didn't jibe, a missing fragment here, a wrong answer there. With Dal and Tiger helping he started back over the sequence of events, trying to make sense out of them, and came up squarely against a blank wall.

The things they had done should have worked; instead, they had failed. A specific antibody used against a specific virus should have destroyed the virus or slowed its progress, and there seemed to be no rational explanation for the dreadful response of the uninfected ones who had been inoculated for protection.

And as the doctors sifted through the data, the Bruckian they had brought up from the enclosure sat staring off into space, making small noises with his mouth and moving his arms aimlessly. After a while they led him back to a bunk, gave him a medicine for sleep and left him snoring gently. Another hour passed as they pored over their notes, with Tiger stopping from time to time to mop perspiration from his forehead. All three were aware of the moving clock hands, marking off the minutes that the force screen could hold out.

And then Dal Timgar was digging into the pile of papers, searching frantically for something he could not find. "That first report we got," he said hoarsely. "There was something in the very first information we ever saw on this planet...."

"You mean the Confederation's data? It's in the radio log." Tiger pulled open the thick log book. "But what...."

"It's there, plain as day, I'm sure of it," Dal said. He read through the report swiftly, until he came to the last paragraph—a two-line description of the largest creatures the original Exploration Ship had found on the planet, described by them as totally unintelligent and only observed on a few occasions in the course of the exploration. Dal read it, and his hands were trembling as he handed the report to Jack. "I knew the answer was there!" he said. "Take a look at that again and think about it for a minute."

Jack read it through. "I don't see what you mean," he said.

"I mean that I think we've made a horrible mistake," Dal said, "and I think I see now what it was. We've had this whole thing exactly 100 per cent backward from the start, and that explains everything that's happened here!"

Tiger peered over Jack's shoulder at the report. "Backward?"

"As backward as we could get it," Dal said. "We've assumed all along that these flesh-and-blood creatures down there were the ones that were calling us for help because of a virus plague that was attacking and killing them. All right, look at it the other way. Just suppose that the intelligent creature that called us for help was the virus, and that those flesh-and-blood creatures down there with the blank, stupid faces are the real plague we ought to have been fighting all along!"