"Strange," Guitierrez had said.

"No, like all the others," the medical officer replied, adding that he had heard of other biting incidents: A child in Vasquez, the next village up the coast, had been bitten while sleeping. And another in Puerta Sotrero. All these incidents had occurred in the last two months. All had involved sleeping children and infants.

Such a new and distinctive pattern led Guitierrez to suspect the presence of a previously unknown species of lizard. This was particularly likely to happen in Costa Rica. Only seventy-five miles wide at its narrowest point, the country was smaller than the state of Maine. Yet, within its limited space, Costa Rica had a remarkable diversity of biological habitats: seacoasts on both the Atlantic and the Pacific; four separate mountain ranges, including twelve-thousand-foot peaks and active volcanoes; rain forests, cloud forests, temperate zones, swampy marshes, and arid deserts. Such ecological diversity sustained an astonishing diversity of plant and animal life. Costa Rica had three times as many species of birds as all of North America. More than a thousand species of orchids. More than five thousand species of insects.

New species were being discovered all the time at a pace that had increased in recent years, for a sad reason. Costa Rica was becoming deforested, and as jungle species lost their habitats, they moved to other areas, and sometimes changed behavior as well.

So a new species was perfectly possible. But along with the excitement of a new species was the worrisome possibility of new diseases. Lizards carried viral diseases, including several that could be transmitted to man. The most serious was central saurian encephalitis, or CSE, which caused a form of sleeping sickness in human beings and horses. Guitierrez felt it was important to find this new lizard, if only to test it for disease.

Sitting on the beach, he watched the sun drop lower, and sighed. Perhaps Tina Bowman had seen a new animal, and perhaps not. Certainly Guitierrez had not. Earlier that morning, he had taken the air pistol, loaded the clip with ligamine darts, and set out for the beach with high hopes. But the day was wasted. Soon he would have to begin the drive back up the hill from the beach; he did not want to drive that road in darkness.

Guitierrez got to his feet and started back up the beach. Farther along, he saw the dark shape of a howler monkey, ambling along the edge of the mangrove swamp. Guitierrez moved away, stepping out toward the water. If there was one howler, there would probably be others in the trees overhead, arid howlers tended to urinate on intruders.

But this particular howler monkey seemed to be alone, and walking slowly, and pausing frequently to sit on its haunches. The monkey had something in its mouth. As Guitierrez came closer, he saw it was eating a lizard. The tail and the hind legs drooped from the monkey's jaws. Even from a distance, Guitierrez could see the brown stripes against the green.

Guitierrez dropped to the ground and aimed the pistol. The howler monkey, accustomed to living in a protected reserve, stared curiously. He did not run away, even when the first dart whined harmlessly past him. When the second dart struck deep in the thigh, the howler shrieked in anger and surprise, dropping the remains of its meal as it fled into the jungle.

Guitierrez got to his feet and walked forward. He wasn't worried about the monkey; the tranquilizer dose was too small to give it anything but a few minutes of dizziness. Already he was thinking of what to do with his new find. Guitierrez himself would write the preliminary report, but the remains would have to be sent back to the United States for final positive identification, of course. To whom should he send it? The acknowledged expert was Edward H. Simpson, emeritus professor of zoology at Columbia University, in New York. An elegant older man with swept-back white hair, Simpson was the world's leading authority on lizard taxonomy. Probably, Marty thought, he would send his lizard to Dr. Simpson.

Dr. Richard Stone, head of the Tropical Diseases Laboratory of Columbia University Medical Center, often remarked that the name conjured up a grander place than it actually was. In the early twentieth century, when the laboratory occupied the entire fourth floor of the Biomedical Research Building, crews of technicians worked to eliminate the scourges of yellow fever, malaria, and cholera. But medical successes-and research laboratories in Nairobi and Sao Paulo-had left the TDL a much less important place than it once was. Now a fraction of its former size, it employed only two full-time technicians, and they were primarily concerned with diagnosing illnesses of New Yorkers who had traveled abroad. The lab's comfortable routine was unprepared for what it received that morning.

"Oh, very nice," the technician in the Tropical Diseases Laboratory said, as she read the customs label. "Partially masticated fragment of unidentified Costa Rican lizard." She wrinkled her nose. "This one's all yours, Dr. Stone."

Richard Stone crossed the lab to inspect the new arrival. "Is this the material from Ed Simpson's lab?"

"Yes," she said. "But I don't know why they'd send a lizard to us.

"His secretary called," Stone said. "Simpson's on a field trip in Borneo for the summer, and because there's a question of communicable disease with this lizard, she asked our lab to take a took at it. Let's see what we've got."

The white plastic cylinder was the size of a half-gallon milk container, it had locking metal latches and a screw top. It was labeled "International Biological Specimen Container" and plastered with stickers and warnings in four languages. The warnings were intended to keep the cylinder from being opened by suspicious customs officials.

Apparently the warnings had worked; as Richard Stone swung the big light over, he could see the seals were still intact. Stone turned on the air handlers and pulled on plastic gloves and a face mask. After all, the lab had recently identified specimens contaminated with Venezuelan equine fever, Japanese B encephalitis, Kyasanur Forest virus, Langat virus, and Mayaro. Then he unscrewed the top.

There was the hiss of escaping gas, and white smoke boiled out. The cylinder turned frosty cold. Inside he found a plastic zip-lock sandwich bag, containing something green. Stone spread a surgical drape on the table and shook out the contents of the bag. A piece of frozen flesh struck the table with a dull thud.

"Huh," the technician said. "Looks eaten."

"Yes, it does," Stone said. "What do they want with us?"

The technician consulted the enclosed documents. "Lizard is biting local children. They have a question about identification of the species, and a concern about diseases transmitted from the bite." She produced a child's picture of a lizard, signed TINA at the top. "One of the kids drew a picture of the lizard."

Stone glanced at the picture. "Obviously we can't verify the species," Stone said. "But we can check diseases easily enough, if we can get any blood out of this fragment. What are they calling this animal?"

" 'Basiliscus amoratus with three-toed genetic anomaly,' " she said, reading.

"Okay," Stone said. "Let's get started. While you're waiting for it to thaw, do an X-ray and take Polaroids for the record. Once we have blood, start running antibody sets until we get some matches. Let me know if there's a problem."

Before lunchtime, the lab had its answer: the lizard blood showed no significant reactivity to any viral or bacterial antigen. They had run toxicity profiles as well, and they had found only one positive match: the blood was mildly reactive to the venom of the Indian king cobra. But such cross-reactivity was common among reptile species, and Dr. Stone did not think it noteworthy to include in the fax his technician sent to Dr. Martin Guitierrez that same evening.

There was never any question about identifying the lizard; that would await the return of Dr. Simpson. He was not due back for several weeks, and his secretary asked if the TDL would please store the lizard fragment in the meantime. Dr. Stone put it back in the zip-lock bag and stuck it in the freezer.

Martin Guitierrez read the fax from the Columbia Medical Center/Tropical Diseases Laboratory. It was brief: -

SUBJECT: Basiliscus amoratus with genetic anomaly

(forwarded from Dr. Simpson's office)

MATERIALS: posterior segment,? partially eaten animal

PROCEDURES PERFORMED. X-ray, Microscopic, immunological RTX

for viral, parasitic, bacterial disease.

FINDINGS: No histologic or immunologic evidence for any communicable disease in man in this Basiliscus amoratus sample.

(signed)

Richard A. Stone, M.D., director

Guitierrez made two assumptions based on the memo. First, that his identification of the lizard as a basilisk had been confirmed by scientists at Columbia University. And second, that the absence of communicable disease meant the recent episodes of sporadic lizard bites implied no serious health hazards for Costa Rica. On the contrary, he felt his original views were correct: that a lizard species had been driven from the forest into a new habitat, and was coming into contact with village people. Guitierrez was certain that in a few more weeks the lizards would settle down and the biting episodes won end.

The tropical rain fell in great drenching sheets, hammering the corrugated roof of the clinic in Bahia Anasco. It was nearly midnight; power had been lost in the storm, and the midwife Elena Morales was working by flashlight when she heard a squeaking, chirping sound. Thinking that it was a rat, she quickly put a compress on the forehead of the mother and went into the next room to check on the newborn baby. As her hand touched the doorknob, she heard the chirping again, and she relaxed. Evidently it was just a bird, flying in the window to get out of the rain. Costa Ricans said that when a bird came to visit a newborn child, it brought good luck.

Elena opened the door. The infant lay in a wicker bassinet, swaddled in a light blanket, only its face exposed. Around the rim of the bassinet, three dark-green lizards crouched like gargoyles. When they saw Elena, they cocked their heads and stared curiously at her, but did not flee. In the light of her flashlight Elena saw the blood dripping from their snouts. Softly chirping, one lizard bent down and, with a quick shake of its head, tore a ragged chunk of flesh from the baby.