7 APRIL 2003

7:55 A.M.

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Afresh wave of guilt assaulted Michael as he watched Alexandra Pace help her daughter step from the dock into the boat that would carry them downstream. She’d caught him off guard at breakfast, disarming him with a couple of well-placed barbs and cutting his faith off at the knees.

Well, perhaps he was overstating the case a bit. His faith had proven itself strong enough to support him through the grief of Ashley’s illness and death, so it could certainly withstand the stings of an American woman’s acid tongue.

Still, he had felt woefully unprepared in the face of her ambush. But how could he explain faith to a woman who viewed her life through the unflinching eyes of reason? She’d spoken of grief—and he had no trouble believing she knew it well. Beneath that glib tongue and defensive posture, some sorrow had hardened her heart to everything but her daughter.

He ought to keep his distance, set a defensive perimeter around the woman and not venture closer than ten feet, but something about her piqued his interest. In less than five minutes’ conversation she’d proven herself an expert on prion diseases in an era when few physicians knew much about them; in less than an hour she’d demonstrated her admirable devotion to her daughter. So she did have a soft side.

With luck, he might get better acquainted with it.

Blowing out his breath, he dropped his pack to the dock and looked around. Their traveling party of thirteen—an unlucky number, if one put stock in such things—was taking two boats downriver to Libertad, a small village near the spot where Ya-ree had stepped out of the jungle. From Libertad the team would set out on foot. They had no idea how long it would take to find Ya-ree’s village, but a man with a perforated bowel could not have walked for more than twenty-four hours. After learning that information, Alejandro Delmar, the Brazilian tracker, estimated they would need five or six days to find the settlement they sought.

Just after the group finished breakfast, Delmar had spread a map of the area on a table and run his fingertip over a series of grids. “I have a GPS device,” he said, pointing to a box hanging from his belt. “We will go into the jungle and move through the center of each square on this grid, looking for trails.”

“What if there are no trails?” Deborah Simons interrupted.

Michael brought his hand up to cover a smile. The large-boned entomologist from Texas was as outspoken as Alexandra, but she lacked Dr. Pace’s bite. He had liked her immediately.

“If there are people in the area,” Emma answered, “we’ll find trails. The jungle is impossible to penetrate without them.”

Cocking his head to one side, Delmar tapped the map. “If we find nothing on the first pass, we will double back to a fixed location here, then press forward at a different angle, making a path through the jungle until we have completely covered the target area.”

He tilted a brow at Carlton, who grunted in approval. “A good plan, Delmar. It shouldn’t take long. If there are Indians living in the area, we’ll find them. And if they have the cure we’re looking for, well—” his grin widened—“we’ll sweet talk it out of them, right?”

The anthropologist had groaned softly at that comment, but the group broke up and moved out to prepare for the journey.

Now Michael smiled in chagrin, mentally comparing the tiny compass in his bag with Delmar’s GPS, which could bounce a signal to a satellite in space, then reveal the latitude, longitude, and sometimes even the altitude of the device. Duke Bancroft and Raul Chavez also carried GPS devices, so the odds of anyone in their party becoming lost were virtually nonexistent, as long as they remained with the group.

He moved back as Louis Fortier, the effervescent French perfumer, stepped into the boat and took a seat on the bench next to Alexandra and Caitlyn. Duke Bancroft sat at the head of the boat, and Valerik Baklanov, the Russian, sat at the back with Milos Olsson and Tito, one of the young men from the lodge. Tito and Hector, regular “drivers” for Yarupapa, had agreed to take the group to Libertad and pick them up when summoned either by radio or messenger.

Michael hesitated on the dock. With a driver and six passengers each, both boats had been comfortably filled, so he was literally the odd man out. He glanced back at the second boat, then decided that given Caitlyn Pace’s small size, logic dictated that he ride with the first group.

“Hope I’m not crowding anyone,” he said, taking the single remaining seat on the right side of the boat. Settling his arms on the pack in his lap, he found himself almost knee-to-knee with Alexandra. She said nothing, but slipped one arm around her daughter while using the other to settle her straw hat more firmly upon her head.

Michael drew a deep breath. If the woman didn’t defrost a little, this trip to Libertad would be very chilly indeed.

Propelled by Tito’s oar, the boat moved away from the dock. When the young man started the outboard motor, Michael felt the vibration run through the boards beneath his feet. Scooping out two holes in the muddy brown water, the engine puttered steadily at the stern as they left the lodge behind.

For ten minutes they rode without speaking, each of them silently drinking in the sights of the river. Michael leaned back, propping an elbow on the gunwale, and marveled at the high-water marks on passing trees—amazing, that the river could rise and fall several meters within a matter of months.

Caitlyn Pace, imbued with a child’s natural exuberance, quickly put an end to the silence. “Look, Mom—see those dots on that tree? They’re fruit bats. They’re sleeping now, but they’ll fly away at sunset.”

Michael suppressed a smile when Alexandra shivered dramatically at the thought.

Caitlyn turned on the bench, pointing out the distant gray rises of river dolphins, the calling macaw, and the occasional serpentine trail of a snake in the water. The girl was a virtual sponge, Michael decided, absorbing everything she saw and heard. While her mother had been bouncing around in the treetops, this girl had been learning from the guides at the lodge.

Caitlyn giggled when they passed an orchid-laden tree with marmosets scampering in its branches. As they slowed to maneuver around a submerged trunk in the river, Caitlyn reached out to pluck a green pod from an overhanging branch.

Alexandra put out a warning hand. “Be careful, honey.”

“It’s okay, Mom. Lazaro called this the medicine tree. And he showed me how to do this.” With ease the girl cracked open the pod, then withdrew a yellow husk. “Lazaro said the boys use these for skipping stones—they count the number of skips, then tell each other that’s how many wives they’re going to have when they’re thirty.”

While Alexandra smiled indulgently, Caitlyn cracked the yellow husk, revealing a green seed shaped like a semicircle with scalloped edges. Grinning, she slipped her finger through a natural cleft in the seed, then clamped it on her earlobe.

Grinning at Michael, she lifted her hands to her head in a model’s pose. “Neat, huh? Lazaro said the girls use these for earrings.”

Michael nodded. “It’s aces. A fetching color, actually.”

“And totally free. Lazaro says the medicine tree grows everywhere.”

“The medicine tree?” Alexandra bent to pick up one of the broken husks. “Did he say what else they use these for?”

Caitlyn shrugged. “He only talked about the stones and the earrings. I didn’t ask about anything else.”

“Hey, Olsson,” Alexandra called. She held up the green seed. “Recognize this?”

The botanist grinned. “Enterolobium cyclocarpum, or elephant’s ear tree. Very common in these parts.”

Michael watched as Alexandra pulled one of the seeds from her daughter’s earlobe, then sniffed at it. “They grow everywhere?”

“That’s what he said. Look—they’re all along the riverbank.”

Michael turned. Caitlyn was right—apparently the tree was as plentiful as mosquitoes.

When he turned again, Alexandra’s eyes were abstracted and distant. “If they’re abundant. . .”

“They’re probably not what we’re looking for,” Michael finished her thought. “But it wouldn’t hurt to test a sample, would it?”

They rode in silence for a while. When Caitlyn hung one arm over the boat to trail her fingertips in the water, Michael asked, “Aren’t you worried about piranha?”

She grinned. “Lazaro says they won’t bite you unless you’re bleeding. He’s never been bitten and he swims in the water all the time.”

“She’s braver than I am.” Alexandra met Michael’s eye. “I cringe when I think about all the creatures living in this river. And when I remember that it also serves as a sewer for nearly every family in the jungle—” She shuddered again, and this time Michael did not think she was pretending.

Jerking her thumb over her shoulder, she gestured to Baklanov, who was puffing on a cigarette as if his life depended upon it. “Dr. Baklanov specializes in bacteriophages. He would have a grand time analyzing the bacteria and viruses populating this water.”

Upon hearing his name, the Russian coughed, then leaned forward to join in the conversation. “I came here to look for new phages in the canopy.” He gave Michael a conspiratorial smile. “But now that we have arranged to take a side trip, I will gather samples that might contain new phages wherever we find, um, interesting situations. It is not often that a Russian from Tbilisi has an opportunity to study in a tropical forest.”

“It’s not often that I do, either,” Michael answered, glad to find someone willing to engage in relaxed conversation. “I spend most of my time in Iquitos—it’s a nice city, but sometimes the workload drives me mad. We have too many patients and not enough doctors.”

Baklanov rested his elbows on his knees. “I’ve been meaning to ask—what brought you to this place?”

Michael stretched one arm along the edge of the boat. “After my wife died, I took a brief sabbatical. One of my mates suggested a trip to the rainforest—at the time, he could have suggested the moon and I’d have signed on. Anyway, within a fortnight I found myself in Peru. I spent a week in the jungle doing tourist things, then made my way back to Iquitos. I was there, waiting for my flight to Lima, when I decided to see a bit of the city. I wandered around for a while, then stopped into a riverfront café and ordered a pizza and lemonade.”

His voice softened with the memory. “I ate a few slices of pizza and left the rest sitting on the table—didn’t have much of an appetite, I suppose, in the heat. Then the waitress came over and said something in Spanish—the only word I caught was niño.”

“Little boy,” Caitlyn supplied.

Michael smiled. “Indeed. In my confusion, I thought the waitress was asking if I wanted her to wrap up the remaining pizza to take back to my little boy. I tried to explain that I didn’t have any niños, and somehow she realized her mistake. ‘No,’ she said, ‘este niño’—and she pointed to one of the street urchins who’d been trying like the dickens to polish my shoes.

“The truth hit me like a blow between the eyes—the boy was one of the many orphan children who live on the streets of Iquitos. She meant the food for him, and it might have been the only meal he’d receive that day.”

He looked up to see Alexandra watching him, lines of concentration deepening along her brows. Caitlyn was listening with her mouth open in a perfect O, and Baklanov’s eyes had gone damp.

He gave them a rueful smile. “I handed over my plate, and instantly regretted that I’d eaten as much as I did. I ordered a pitcher of lemonade, too, then called the boy over to sit with me while he drank and ate his dinner.”

Shrugging, Michael let his gaze drift over the brown velvet river. “I knew I couldn’t feed every street child, but I could do something to help this one. The poor boys wore old T-shirts and shorts; most had bare feet. They made a living washing tourists’ shoes with river water they carried in empty pop bottles . . . and when they were sick, they had no one to care for them.”

He shifted to meet Alexandra’s eyes. “That’s when I decided to spend a year or two in Iquitos. The people here are so desperate for help, no one protested when I arrived at the hospital and announced that I’d come to work. They found me an office, threw open the door, and suddenly I had more patients than I knew how to handle. Word got around, and soon everyone came to see me—children, old people, Indians, tourists. I’ve been in Peru three years now, and I can’t say I’ve ever experienced what we’d call a routine day back in London.”

Alexandra Pace cleared her throat and looked away.

“Wow.” Admiration shone in Caitlyn’s eyes. “I’ll bet you speak excellent Spanish.”

Michael laughed. “I’m afraid I’m not too keen on languages. My nurse speaks English, though, and translates for me when necessary. The others on staff take pity on me and speak slowly. Sometimes we resort to sign language.”

“Dr. Kenway.” Baklanov adjusted his cap to better shade his face as he turned toward Michael. “I’m interested in these prion diseases you and Alexandra are investigating. I have spent my life researching the invisible world, but I have never encountered these prions you speak of. I wasn’t sure I believed in their existence until Alex showed me photographs.”

Michael crossed his legs, resting one ankle on his knee. “I thought you were an expert on the subject, Dr. Baklanov. Dr. Pace has assured me that you and she are working together on this expedition—”

“Bah! I know nothing!” Baklanov sent Alexandra a look of bewildered incredulity. “Accept this man’s help, my stubborn friend. Leave me to my phages; we will not get in your way.”

Michael stole a brief look at Alexandra—the woman’s cheeks had flushed crimson, yet she continued to look out over the water as if she hadn’t heard a word of the conversation.

Granting her mercy, Michael answered the Russian doctor’s first question. “Unfortunately, Dr. Baklanov, I know about prions from firsthand experience. Still, I can understand your reluctance to accept them.”

“Their structure makes no sense to me.” The Russian knocked the glowing ashes of his cigarette into the river. “Every known living organism uses molecules of nucleic acid to carry information it needs to reproduce, yet these proteins do not contain nucleic acid. How can they reproduce at all?”

Caitlyn screwed her face into a question mark. “Remind me about nucleic acid, please?”

“DNA or RNA.” Grinning, Michael lifted his eyes to meet her mother’s. “How much do you know about how life begins?”

“She knows the truth.” Alexandra waved in a deliberately casual movement. “We don’t talk about birds and bees, for instance. She knows the proper terms.”

“Right.” Deciding to test the woman’s assertion, Michael bent to Caitlyn’s level. “Long ago, biologists used to think tiny little men lived inside human sperm. Using crude microscopes, they actually claimed to have seen these little fellows, or homunculi, as they called them. Supposedly, these little men settled in a female egg cell, ate the yolk, and grew big within the woman’s womb.”

Caitlyn giggled. “That’s crazy. Everybody knows about chromosomes and the double helix.”

Michael looked at her mother again. “How old is this child?”

“Ten,” Alexandra answered, “going on thirty.”

“Quite.” Returning to Caitlyn’s level, Michael continued his explanation. “In time, of course, biologists wised up and began setting things to rights. They finally figured out that cells—and chromosomes— contained DNA, the building blocks that could create a person. Obviously, you know about the double helix that separates when a cell divides.”

Caitlyn shrugged. “I studied all that two years ago.”

Baklanov gazed at the girl in rapt admiration. “Amazing.”

“Well,” Michael continued, “not every part of your body needs the entire DNA sequence—you are also composed of proteins, hundreds of different varieties. These proteins do the mechanical and chemical work of the body, and they are formed from RNA, which comes from DNA. These proteins do not contain nucleic acid, but they do have a proper structure. Imagine, if you will, one of those toy necklaces made of beads that snap together. The pattern in which they are joined affects how they perform in the body.”

He had thought he’d lose her in the complicated explanation, but the girl nodded, thought working in her eyes.

Michael took a deep breath. “A protein, you see, doesn’t reproduce like a virus or bacteria because it’s nothing but bare beads, so to speak. Most of the time proteins are mass-produced by the body, and all of them are normal, snapped together in just the right formation. But occasionally the body will absorb a different protein—one composed of exactly the same materials, but snapped together in a different pattern. From that moment on, all the body’s newly manufactured proteins begin to model themselves after the mutated one. We call the one that causes all the trouble a prion.”

He squinted at Caitlyn. “I’m assuming you know what mutated means.”

“Altered, transformed, transmuted.” She frowned up at him. “But what caused it to be different?”

“I haven’t the faintest idea.”

“No one knows what triggers the mutation.” Shooting Michael a glance of grudging respect, Alexandra entered the conversation. “Some have theorized that the process has something to do with crystals—like ice.”

Baklanov’s forehead crinkled. “Would you mind explaining that one?”

Caitlyn clapped her hands. “I get it! It’s like water—two molecules of hydrogen, one of oxygen. At room temperature, H2O is liquid. Above boiling, it becomes steam. Below freezing, it’s ice. Three different forms of the same molecular composition.”

“That’s close, honey.” Alexandra gave her daughter a smile. “But prions are a little more complicated. The process of crystallization occurs in our bodies all the time. It’s through crystallization that our bodies turn the calcium in milk into teeth and bones. Because the process has been fine-tuned through evolution, our bodies know that teeth require one organic structure while bones need another. There’s an atomic pattern, sort of like a blueprint, that these proteins follow in order to reproduce.”

When Caitlyn blinked, Michael suspected that for the first time in a long time the girl had been handed information she couldn’t instantly absorb.

He bent to peer into Caitlyn’s eyes. “I wouldn’t place much stock in that talk about evolution. I happen to believe it’s blarney.”

“Ignore him, dear.” Leaning forward, Alexandra curved her upturned palm into a cup. “If you had a handful of marbles and you dropped them in my palm, how would they stack up?”

As Caitlyn stared at her mother’s hand, Michael could almost see her mental computations—three marbles across the fingers, perhaps four across the palm, the next row would stack in the concave spaces, a third row might fit before they began to spill over the edge of her mother’s thumb. . .

Caitlyn made a face at the imaginary marbles. “I figure you could stack thirty-three before they would begin to fall out of your hand.”

Alexandra laughed. “That’s good, honey, but I asked you how they would stack up. In order to figure the amount, you had to visualize how they would lie in my palm, right? So the answer is more oblique— the arrangement of the stack would depend upon the layout of the bottom layer.”

Confusion clouded Caitlyn’s eyes for a moment, then her face brightened. “Of course!”

Alexandra turned to Baklanov. “Crystals reproduce according to an atomic template. If that template is mutated, the resulting structures will pattern themselves after the mutation. We think that’s how prions reproduce. One foreign template enters the body—probably from the ingestion or insertion of foreign prions—and every protein the brain produces from that point is also mutated. These proteins do not function properly, so brain cells begin to die. In time, the death of these cells creates holes in the brain. And without a brain. . .” Her eyes darkened as her voice faded away.

Michael snapped his fingers as a thought occurred. “It’s like Cat’s Cradle!”

Three perplexed faces swiveled toward him.

“A Kurt Vonnegut novel—I read it during my adolescent science fiction phase. In the story, a scientist creates a new variety of ice that melts at 114.4 degrees Fahrenheit. Trouble is, whenever the stuff—he called it ice-nine—touched anything liquid, it turned the liquid into ice-nine.”

Caitlyn grinned. “Cool.”

Michael shook his head. “Not really. One character touched the ice-nine to his tongue, and his body—composed mainly of water, as all our bodies are—immediately froze solid. When the ice-nine encountered the ocean, all the seas and everything in them froze. Every river that ran to the ocean, every raindrop that touched the damp soil turned to ice-nine. That scientist’s little invention spelled the end of life on earth.”

Alexandra gave him a brief, distracted glance. “I haven’t read that book, but I can appreciate the metaphor. Yes, prions might operate in the same way. Depending upon the pattern, they can clog the heart or the brain, and in time the living organism is . . . well, it’s too diseased to function.”

Two deep worry lines appeared between Caitlyn’s brows, but she didn’t look up at her mother. Instead she turned and studied the riverbank, signaling through body language that she had grown bored with the conversation.

Alexandra’s eyes swept over her daughter’s form, and for an instant Michael thought he saw a flicker of pain in those expressive depths. But then she looked toward the shore, too, her hand rising to adjust the brim on her straw hat.

Taking his cue from the women, Michael stared at the floor and surrendered to the silence that had settled over the boat. He couldn’t help but wonder, though, why a woman as bright and competitive as Alexandra Pace would delve into a frantic study of diseases that until recently had struck fewer than one person in a million.