Like the twisted strands of mutant chromosomes, an insidious alien conspiracy winds its way through the entire Alpha Quadrant, just as it stretches across several years of Starfleet history -- beginning near the very start of Captain Picard's command of the "Starship Enterprise(TM) !" It is only the first year of the "U.S.S. Enterprise(TM) "-D's ongoing mission when a virulent epidemic strikes the populace of Archaria III, endangering the lives of thousands and provoking acts of mob violence against those believed responsible for the spread of the disease. While Data and Natasha Yar team up to uncover the true origins of the virus, Dr. Crusher finds that the implacable sickness resists all her efforts to find a cure. The desperate quest for a cure becomes even more urgent when Deanna Troi succumbs to the dreaded plague...again and again.

**

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Chapter One

Stardate: 41211.0 Captain's Log, Supplemental

The Enterprise continues on its mission to Archaria III, a planet jointly colonized by humans and Peladians. A new disease has cropped up, terrifying the inhabitants. So far, more than five thousand cases have been confirmed.

The only drug at all effective in treating this disease is a rare compound called Tricillin PDF, which seems to prolong life, though only for a week at most. The Enterprise will deliver a supply of the drug, quarantine the planet, then stay to oversee research into finding a cure.

" -- And render whatever aid the Archarians require until the emergency is over," Captain Picard said, leaning forward at the conference table and gazing at each of his senior staff in turn.

William Riker, Geordi La Forge, and Worf looked uncomfortable at the mention of the plague, and he didn't blame them; he had always felt ill at ease when faced with intangible dangers. Deanna Troi looked deeply concerned, and Dr. Crusher looked...intrigued? She has dealt with plagues before, Picard reminded himself. She knows how to contain them.

The persistent low rumble of a starship at maximum warp filled the room. None of his crew spoke. They feel the tension building already, he thought.

"Captain," Dr. Crusher finally said, "I may have to bring samples of this virus aboard the Enterprise for study, and perhaps a few patients."

"Understood, Doctor. So long as all necessary security precautions are maintained, I see no problem. In the meantime" -- he slid a data padd across the conference table to her -- "the doctors of Archo City Hospital have prepared a full report, which you may find useful."

"Thank you." She pulled the padd in front of herself and began skimming the opening remarks.

"Something else is troubling you, sir," Deanna Troi said softly.

Picard hesitated, then gave a curt nod. Best to get it out in the open. "What disturbs me most is the thought that this whole problem may be of our own manufacture...a biological weapon."

"Impossible -- how could that be?" Riker said, shaking his head dismissively. "Legalities aside, it's against everything the Federation stands for!"

"We do have treaties with most sentient races which prevent the development and use of biological weapons," Data said. "With all due respect, sir, the deployment of a genetically designed plague on a remote agricultural world such as Archaria III seems highly unlikely."

"Not necessarily," Picard said. He cleared his throat. "Archaria III is in many ways a throwback to human civilization two or three hundred years ago. It was settled by religious zealots early in the twenty-second century, and although they have largely come into the Federation's fold, old prejudices and resentments still bubble to the surface from time to time." The room was quiet for a moment while Picard allowed his point to sink in.

Riker finally broke the silence. "Sir, if I may ask, what is it that leads you to conclude this disease is a weapon?"

"Might be a weapon, Number One. A radical political group called the Purity League claims the plague is an act of God against 'blasphemous unnatural unions.'"

Riker gave him a blank stare. "Sir?"

Picard cleared his throat. How to phrase this delicately. He said, "The Purity League is opposed to interspecies mating -- 'mixers' as they call such people."

Again the rumble of the ship's engines filled the room. They can't believe it, either, he thought. Humanity is supposed to be beyond such prejudices.

He noticed that Deanna Troi, half human and half Betazoid herself, hid her inner feelings behind a mask of professional calm. He would have given a lot to know her true reaction. Undoubtedly she was even more shocked and horrified than he had been.

To think that some humans are still capable of such petty resentments...

He forced himself back to the problem at hand. "Mixers -- or anyone else suspected of adulterating the purity of the human race -- are treated as second-class citizens in many places on Archaria III," he continued. "Officially such prejudices are prohibited, of course, but in the backwater towns discrimination apparently still runs rampant. Only in the half-dozen large cities do humans and Peladians work and live together with something approaching harmony. In the country, things have apparently become so bad that most full-blooded Peladians now live in isolated enclaves surrounded by their own kind."

Riker said, "That sounds like a ghetto system."

"It is. Those of mixed heritage are even less fortunate, since they belong fully to neither the human nor the Peladian world. They were relocating to the cities in record numbers -- until the plague struck. Now they're fleeing into the countryside once more, living like vagabonds in tent camps." Picard looked down at his clenched, interlaced fingers resting uneasily on the table. He didn't bother to feign relaxation. Sometimes it was good for the crew to see him share their anger.

Deanna Troi asked, "How many people of mixed blood are on the planet?"

"Nobody is quite sure. Estimates range from between 150,000 and 200,000 people. Obviously, those mixers who most closely resemble humans hide the truth to avoid conflict with the Purity League."

Data said, "I am aware of the Purity League, sir. The Federation has monitored their activities for many years, but has deemed them a minor nuisance with little actual influence."

"Their influence is growing," Picard said firmly. The private reports he had read gave alarming statistics; according to confidential surveys, fully half of the planet's human population harbored feelings of support for the Purity League, though the League's actual membership numbers were open to conjecture. It was certainly in the tens of thousands if not the hundreds of thousands.

He went on. "The Purity League's leader, Father Veritas, is using the plague as a rallying point for anti-alien sentiment. Apparently Veritas is responsible for inciting dozens of race riots in the last few months. The whole planet is in turmoil. The nonhuman population -- and especially the partly human population -- is running scared. The plague's growth has only served to make the situation worse." "Veritas," indeed, he thought, grimacing. If ever there was a misnomer...

"Sir," said Deanna Troi, "Archaria III has a long history of interspecies problems, including wars, assassinations, and racism. Its history is part of several planetary evolution courses at the Academy. I believe everyone here has studied it to some degree."

A general murmur of agreement came from the rest of his senior staff. Picard found himself surprised -- it hadn't been part of the curriculum when he had studied at the Academy -- but he was pleased. They're keeping up with the times.

"That is correct, sir," said Data. "It was settled in 2102 by a human sect of religious fundamentalists called the Brotherhood. Seven years later, these human settlers encountered Peladian settlers, who had colonized the planet almost simultaneously."

Picard had never seen a Peladian and knew little about them, beyond the fact that they were humanoid, militant about privacy, and generally considered pacifists...except when provoked.

Data went on, "After a series of small wars, as the two sides got to know each other, peaceful relations and coexistence began. According to the information I have accessed, with the increasing agricultural importance of Archaria III their differences were largely put aside, in favor of economic cooperation."

"That is the public story," Picard said. He folded his arms and frowned a bit. "There have always been tensions. Until Father Veritas and the Purity League burst onto the scene sixteen years