Just then Selar’s console beeped, indicating that the analysis on the data she’d brought back from Tenjin was complete. She forwarded it to the others. “However, Dr. Crusher, I suggest you add at least one more active culture to your list. This one is a carcinoform.”

Uhura sighed. “In English, please.”

“The pathogen collected on Tenjin is a virus that mutates into a form of cancer,” Selar explained. “It tracks with the Gnawing/R-fever neoform in all other respects. Patients presented to their physicians with cough, shortness of breath, fever, respiratory compromise, unilateral or bilateral infiltrates in the lungs, and symmetrical alveolar spread. Mortality rate was one hundred percent.”

“Sounds like our bug, all right,” Crusher said morosely.

“With one notable differentiation,” Selar said. “Autopsies revealed that every major organ was riddled with cancerous tumors…”

“There goes my appetite!” Sisko said quietly.

“…despite the fact that the disease vector indicated a contagion which was passed from one person to another in close proximity.”

“How many dead?” Uhura asked, ready to add this new death toll to the others.

“Sixty-four,” Selar said.

“A cancer that’s contagious?” Uhura frowned. “How is that possible?”

“Ordinarily, it is not,” Selar explained. “But we are dealing with an artificial neoform which, hypothetically, could be. Both viral infection and cancer are inflammatory processes.”

Before Uhura could ask her usual question, Selar went on.

“Most disease processes, from cancer to the common cold, are the result of normal cells going awry,” she explained. “Either a ‘germ’ such as a cold virus or a cancer-causing agent invades the body from the outside, or healthy cells can mutate for a number of reasons—exposure to radiation, environmental pollutants. The body contains cells known as natural killer cells, which recognize these altered cells as invaders and attempt to destroy them.

“The resulting ‘battle’ is what causes inflammation. The patient exhibits fever, in the case of a virus, or other symptoms with the onset of cancer. If the NK cells win, these symptoms abate and the patient lives. If the mutated cells win, the body succumbs and the patient dies.”

“And you’re telling me this process is the same for cancer as it is for a head cold?” Uhura asked skeptically, making sure she had it right.

“Superficially, yes. Where cancers differentiate is that once they have established themselves in the host, they recruit healthy cells in order to colonize and grow. Tumors, left untreated, will create their own blood vessels and divert the blood supply from healthy tissue. They will then proceed to crowd out and scavenge healthy cells in a lung or liver or pancreas or in blood or bone until the healthy cells cannot function, the organ or system breaks down, and the patient dies.

“It is my hypothesis,” Selar concluded ominously, “that someone, whether by design or accident, has discovered that grafting the Gnawing onto R-fever, possibly with other factors, can sometimes cause the resulting virus, once it is introduced into a host body, to mutate into a form of cancer. The cancer itself is not contagious but, because the virus is, the end result is the same.”

“And it has somehow managed to spread in an enclosed environment like Tenjin,” Uhura said.

“Correct.”

No one said anything for a few minutes. Uhura’s fingers ticked over her console, totting up all the casualties to date.

“We’ve also had a dozen new cases reported on Cestus III,” she reported, “and a possible outbreak on…” Her voice trailed off just in time to hear Crusher ask Selar something about “squeak tests.”

Uhura sighed again. “Squeak tests?”

When Zetha first volunteered to help Selar in the lab, the Vulcan had taught her how to perform viral squeak tests.

“Viruses emit high-frequency sounds,” she had explained, setting up the simple wave transmitter that would do the job. “And each virus has its own distinct sound. A single copy of a stable virus can be detected in a biosample and identified on the basis of its unique sound. Do you understand so far?”

Zetha nodded. Entities so small that they were invisible, existing inside every living thing, some of them powerful enough to kill? Science or sorcery, it was all one to her. If they could kill, why couldn’t they sing as well?

“How does it work?” she asked, indicating the transmitter, insatiably curious, wanting to know everything. Too, pragmatically, the more she learned, the more useful she could be.

Selar, who enjoyed instructing anyone so clearly eager to learn, explained.

“Quartz crystals transmit radio signals. When coated with particles of a virus we wish to identify and exposed to an electrical field, they will vibrate until the virus detaches and shakes free. When it does so, it emits a burst of sound.

“The crystal resonates to the sound and records it as an electrical impulse. Humans cannot hear these sounds, and therefore must rely upon reading the recorded impulse. But most fall within the range of Vulcan hearing, therefore speeding the process.”

“But—” Zetha started to say, then stopped. She was not a Vulcan, but she could hardly say she was a Romulan after a lifetime of being told she was not.

It had occurred to her, once she stopped trembling and settled into the hovercar behind the silent aristocrat whose name she still did not know, that if he had in fact traced her through her codes, he also knew her origins, and which part of her was not Romulan.

It had occurred to Koval as well. In the ensuing months, he would taunt her with it.

“Don’t you want to know your codes? To know who spawned you, what your parents were?”

She did, but she didn’t, not from him. She couldn’t trust him to tell her the truth, and what she wanted above all else was not to be beholden to him.

“No,” she said.

“I don’t believe you,” he had said with his smug little smile. “If you volunteer for a mission, I will tell you. You will know your place before you die.”

She had shrugged. “If I die for the Empire, I’ll be an honorary Romulan after death,” she reminded him, making sure she was beyond arm’s length before she finished her thought. “By then, though, I doubt I’ll care.”

“I am not a Vulcan,” she told Selar, “nor a Romulan. I—”

In answer, Selar placed a sample virus in the detector and activated it. Its almost inaudible hum grew in intensity as the crystals shook faster and faster. There was a single burst of noise—which sounded to Zetha like a tiny, abbreviated shriek—then a winding down to silence as Selar shut down the device and the crystals ceased their vibration.

“Did you hear that?” she asked Zetha.

“Yes.”

“Can you distinguish it from this?” Selar replaced the contaminated crystal, treating the new one with a fresh viral sample and activating the device. This time when the virus shook free, the sound Zetha heard was more like the snap of a twig. She told Selar this.

“The first was the neoform, the second a mutated herpes virus,” Selar explained. Was there a tinge of pride in her voice, pride in Zetha’s accomplishment? “A human would hear nothing but the vibration of the crystal. You hear like a Vulcan. That is sufficient for our purposes.”

Selar had taught her to codify a number of viruses. By now she could identify the Gnawing neoform by its sound, distinct from anything else Selar could test her with. The sense of accomplishment was something new and, as she listened to Selar explaining the process of squeak testing to Uhura, she savored it.

Albatrossslipped into the moil of traffic above Tenjin as the planet’s orbit took it out of Federation space into the Zone. Deftly Sisko adjusted her trajectory until she was running upstream against the flow of Federation-registered vessels moving grudgingly back into their own space, until he had maneuvered her into the queue of nonaligned vessels waiting to cross into the Zone, then slowed the old girl to station keeping. He could feel more than see Tuvok’s quizzical look.