Kate watched the new series of MR images and flickering data columns with eyes that did not blink. When it was finished she sat in silence for a full minute.

“Kate,” whispered Alan. His voice was almost reverent. “What's going on here?”

Kate's eyes never left the screen. “I don't know,” she said at last. “I honest to God do not know.” But somewhere, deep in the creative subconscious that had made her one of CDC's finest diagnosticians, Kate Neuman did know. And the knowledge both scared her to death and filled her with a strange exhilaration.

Kate Neuman's home was in a high meadow six miles up Sunshine Canyon above Boulder. Kate had always disliked canyonsshe hated the lack of sunshine, especially in winter, and being at what she considered the mercy of gravity if any boulders decided to dislodgebut the road climbed out of the broad swale of Sunshine Canyon and ran along high ridgelines miles before it reached the turnoff to her home. She considered the location of her home almost perfect: high meadows laced with aspen and pine trees swept away. on either side, the snowcapped summits of the Indian Peaks section of the Continental Divide loomed up ten miles to the west, and at night she could look out the gaps in the Front Range south of the Flatirons and see the lights of Boulder and Denver.

She and Tom had bought the home the year before their breakup, and while they had used her income to secure the mortgage and pay the down payment, Kate would always be grateful to Tom for suggesting they look in that particular area for a house. The structure itself was large and modern but it blended into the rocks and trees of the ridgeline, its windows framed views in all four directions, there was a wonderful patio from which she could look downhill toward the Flatirons, and while there was only a handful of houses in the sixhundredacre residential ranch, the area was guarded by a security gate which could be unlocked only by the residents after a visitor contacted them via intercom. These visitors were usually shocked by the roughness of the gravel road beyond that security gate. The yearround residents there all owned fourwheeldrive vehicles to cope with winter snows at the seventhousandfoot level.

On this July morning one week after her discussion with Alan; Kate rose, jogged her usual threequarters of a mile on the loop trail behind her home, showered, dressed in her usual casual outfit of jeans, sneakers, and a man's white shirt for CDCshe wore a suit or dress only when a VIP visit or travel was inflicted on herand had breakfast with Julie and Joshua. Julie Strickland was a twenty-three-year-old graduate student who was currently working on her PhD dissertation on the effects of pollution on three species of flowers found only on the alpine tundra. Kate had met Julie three years earlier through Tom; the younger woman had traveled with Tom's Mountain Challenge Tours for an entire summer of hiking and camping above treeline in some of Colorado's most inaccessible regions. Kate was fairly certain that Julie and Tom had enjoyed a brief fling that summer, but for some reason the fact never bothered her. The two had become friends soon after meeting each other. Julie was quiet but enthusiastic, competent and funny. In exchange for watching Joshua five days a week, Julie had her own section of Kate's five-thousand-square-foot house, was free to use Kate's 386e PC with its CDROM memory for her thesis when Kate was at work, had weekends free for her field trips, and received a token salary that allowed her to buy gas for her ancient Jeep.

Both women enjoyed the arrangement, and Kate was already worrying about the winter when Julie would be finished with her dissertation. Always sympathetic to the plight of working mothers forced to scramble for daycare, Kate now had nightmares about finding adequate care for Joshua. But on this beautiful summer morning, the sun already high above the plains and free of the rim of foothills to the east, Kate put the worry out of her mind as she ate her bran flakes and fed Joshua his cereal.

Julie looked up from her section of The Denver Post. “Are you taking the Cherokee or the Miata to work this morning?”

Kate resisted a smile. She had planned to take the red Miata, but she knew how much Julie loved to drive the roadster down the canyon. “Mmmm . . . the Jeep, I think. Did you have any shopping to do before you dropped Josh off at CDC?”

At the mention of his name, the baby smiled and banged a spoon on his tray. Kate wiped a bit of excess cereal from his chin.

“I thought I'd stop by the King Soopers on Table Mesa. You sure you don't mind me driving the Miata?”

“Just be sure to use the baby seat,” said Kate.

Julie made a face as if to say, Of course I will.

“Sorry,” smiled Kate. “Maternal instinct.” She said it as a joke but instantly realized that this was precisely what prompted such obvious comments.

“Josh loves the convertible,” said Julie. She took her own spoon and pretended to eat some of the baby's cereal. Joshua beamed his appreciation. Julie looked at Kate. “You want him there right at eleven?”

“Approximately,” said Kate, glancing at her watch and clearing her dishes. “We have the MR equipment reserved until one, so it's all right if it's a few minutes after . . . .” She gestured toward Joshua's unfinished cereal. “Do you mind . . . “

“Uhuh,” said Julie, exchanging goofy expressions with the baby. “We like to eat together, don't we, Pooh?” She looked back at Kate, oblivious to the drop of milk on her nose. “This MR stuff won't hurt him, will it?”

Kate paused by the door. “No. It's the same procedure as before. Just pictures.” Pictures of what? she asked herself for the hundredth time. “I'll have him home in time for his nap.”

It was less fun driving the Cherokee down the winding canyon road than doubleshifting the Miata through the turns, but this morning Kate was so lost in thought she did not notice the difference. Once in her office she asked her secretary to hold all calls and put a call through herself to the Trudeau Institute in Saranac, New York. It was a small research facility, but Kate knew that it did some of the best work on effector mechanisms of cellmediated immunity relating to lymphocyte physiology. More than that, she knew its director, Paul Sampson.

“Paul,” she said when she had got past receptionists and secretaries, “Kate Neuman. I've got a riddle for you.” She knew that Paul was a sucker for puzzles. It was a trait that he shared with quite a few of the best medical researchers.

“Shoot,” said Paul Sampson.

“We have an eightandahalfmonthold infant found in a Romanian orphanage. Physically the child looks about five months old. Mental and emotional development seem normal. Physically we see intermittent bouts of chronic diarrhea, persistent thrush, failure to thrive, chronic bacterial infections as well as otitis media. Diagnosis?”

There was only the slightest hesitation. “Well, Kate, you said it was a riddle, so AIDS is out. And that would be too obvious given the Romanian orphanage. Something interesting, you say.”

“Yep, “ said Kate. On the greenbelt below her CDC window, a family of whitetailed deer had come out to graze.

“Was the workup done in Romania or here?”

“Both places,” said Kate.

“OK, then we have some chance of reliability.” There was a pause and Kate could hear the soft sound of Paul chewing on his pipe. He had given up smoking the thing almost two years earlier, but still played with it when he was thinking. “What was the T and Bcell count?”

“Tcell, Bcell, and gammaglobulin levels almost did not register,” said Kate. The data was in the file on her desk but she did not have to refer to them. “Serum IgA and IgM were markedly decreased . . . .”