First captain, now doctor!Sisko thought, trying to hold a deadpan in the face of his most recent promotion.

Thamnos’s beady little eyes lit up momentarily. “Are you from the Journal?”he asked hopefully. Suddenly the dread that had set in after his last conversation with Koval seemed lifted from his shoulders. If someone from the Federation side was willing to foster him, maybe he was safe after all.

Tuvok did not exactly answer the question. “There is another physician in our party who would be better able to address your research. May I summon her?”

Not many men can affect a swagger standing still. Thamnos somehow managed it. “Sure. Be happy to talk to her. Tell her to beam on in.”

Selar’s arrival alone might not have set him off. But something about Zetha’s presence made him suspicious.

“You’re a Romulan,” he said.

Before Zetha could answer, or even decide what to answer, Thamnos began to laugh.

“Okay, I get it! You’re not from the Journal.You’re not from the Federation side at all. I thought he’d come himself, but this is even better. He wants me to test it on you, to back up my article to the Journal.Of course, it all makes sense now…”

His voice and manner grew suddenly manic as he pushed past Sisko and went rummaging amid the debris in the corner until he had scattered all of it to reveal a case of datachips, which he set beside the jury-rigged computer, shoving the jars of hiloponaside.

“Oh, he’s clever! He doesn’t come himself, he sends one of the seeds…” Thamnos was muttering near-hysterically, fumbling through the chips in search of a particular one. “Let’s see, which seeding was it? This one? No. Perhaps this one…let’s see…yes, I think this is it.”

Silently Sisko gave Tuvok an inquiring look. Recommendation?the look said. Do we let him run amok or do we corral him now before he tries to destroy evidence?Tuvok shook his head imperceptibly: I recommend we ascertain what it is he is searching for first.

Thamnos inserted a datachip into the interface. “Computer, correlate retina scan of subjects present with extant files.”

The computer answered him with a code, and Thamnos turned to Zetha smugly. “I knew it! Sample 173. The photo on file makes it look like you have freckles, though. Or is that part of your cover?”

Perplexed, Zetha looked from Selar to Tuvok to Sisko, then back to Selar. “What is he talking about?” she demanded.

“I believe,” Selar said, “he has just provided us with the source of the disease vector.”

Cretak had read Koval’s character correctly. Knowing Tuvan’s Syndrome ran in his family, he had been obsessed with illness—and immunity to illness—all his life. When it first occurred to him what a marvelously versatile illness the Gnawing could be, he recalled what most people had forgotten—that some rare few Romulans were immune to the disease. Once his scientists were able to tell him why—possession of a particular rare gene sequence, extant in less than one tenth of one percent of the population—the rest seemed self-evident.

At first he thought he would simply gather together as many of those with the immunity sequence as possible, secretly infect them with the Gnawing, then scatter them like seeds throughout first the worlds on his side of the Zone, then on certain worlds on the Federation side where vulcanoids were common. He would choose as his “volunteers” Romulans who traveled frequently, many of them his own operatives.

The first stage would have the effect of spreading panic and compelling both his Empire and the other side to accuse each other of biological warfare, always a good ploy for keeping the balance of power unbalanced. Anything that sent the Federation side into a frenzy, as long as it was done subtly, was something Koval’s superiors welcomed. Many in the Tal Shiar, as well as the military and the Senate, hungered for an end to the Empire’s half-century of self-imposed isolation, and a return to expansionism. If Koval’s scheme worked on this level, he could present the expansionists with a game plan for conquering worlds and eliminating their indigenous populations without deploying a single warbird or firing a single shot.

So, how to disguise the Gnawing, and render it dormant until its purveyors could be spread across two quadrants? That was the easy part. When carried by the immunes, it could incubate for weeks, sometimes months, before spreading. Koval’s physicians did not know why the incubation period varied from one immune to another, but it wasn’t that important to them. The difficult part was not making the vector so obvious that it attracted attention too soon.

Then there was the awkwardness of having important Romulans suspected of being carriers. It was at this juncture that Koval began not only training the ghilikwho were already members of his expendable cadre, but searching the Imperial Census files for those who lived in the back streets and whose disappearance would go largely unremarked. The day he cornered Zetha and Tahir in the alley near the cemetery had been only one of many.

Tahir was not an immune, and so of no use to him. But Zetha, once she had been injected with a series of “nutritional supplements” which, had Selar been there to examine them, she would have recognized at once as Catalyst, became Sample 173. The rest was only a matter of time.

Sisko cleared his throat. The annoying dry cough, which had not bothered him while he and Tuvok had at first been poking around among Thamnos’s belongings, had returned. “What are you saying?”

“Oh, come on, don’t play innocent with me!” Thamnos had deactivated the computer, closed the case full of datachips. “He’s more clever than I thought he was. I never realized he had humans and Vulcans in his employ, but then why wouldn’t he? He has the resources. But as soon as I saw her, I knew. All right, you’re branching out on your own, trying to get to the vaccine before he does. I know how that works. Fine, no problem. Only take me with you. He’s as much as threatened to kill me. You have a ship? I want out of here, and fast. I give you the vaccine, you take me with you. Deal?”

“You have perfected an actual vaccine?” Selar asked. “Derived from hilopon,as described in your paper to the Journal?”

Beside her, Zetha had covered her mouth with her hand and was backing away from all of them.

“Sure!” Thamnos said brightly. “Not here. Of course I wouldn’t keep it here. I knew this would be the first place he—or you—would look for it. It’s in a safe place. But I need to go alone. If any of the villagers spotted any one of you, even a human…they’re suspicious enough of strangers, but your clothes…”

“Your vaccine,” Selar said. “Will it work offworld?”

Thamnos’s eyes shifted from side to side.

“I don’t think you’re going anywhere,” Sisko said softly.

He nodded to Tuvok, who moved, catlike, encircling Thamnos’s neck with one long arm, the fingers of his other hand set at the precise point on his shoulder where the briefest pinch would take him down. Thamnos, recognizing the maneuver, did not fight.

“You knock me out, you don’t get the vaccine,” he said. “And you really don’t want to waste any time, you know. You’re all going to need the vaccine very soon. If it isn’t already too late.”

“What the hell are you talking about?” Sisko demanded, moving toward him ominously. He wasn’t sure what he’d do once he got there, but he made the move anyway.

“How long have you had that cough?” Thamnos demanded. He jerked his chin toward Zetha. “She’s the carrier, don’t you see? She’s immune, but she’s been incubating the disease for months. Once it’s triggered, you’ll all get it. That cough tells me you already have!”

It wasn’t a collapse, exactly, Uhura insisted. She’d gotten up from her desk while she was talking to Crusher, and simply misjudged her footing. The fact that she was walking across a level floor that suddenly seemed to undulate and buckle beneath her was beside the point. She was fine, really.