"Happens all the time," he told her. "One wrong turn around here and you can wander for twenty minutes before you find the lobby. Come on-I'll show you."

He walked along beside her, made a left turn then a right, and a moment later they were back in the main lobby. "Thank you," Sharon said as the guard held the door open for her. His fingers touched his hat politely and he turned away. Her heart pounding, Sharon stepped out into the chilly fall afternoon and scanned the parking lot for the station wagon.

It wasn't until she was well out of sight ofTarrenTech that she pulled the car over to the side of the road, left the engine idling, and reached for the purse she'd dropped on the floor in front of the passenger seat.

Her fingers trembled as she opened the bag and pulled out the first of the two objects she'd removed from the box by the elevator.

It was a tiny white mouse, weighing no more than a couple of ounces.

It was dead, its body stiff with rigor mortis.

Sharon gazed at the tiny corpse for a moment, then carefully laid it on the car seat next to her.

The other object was larger, weighing nearly half a pound. It looked very much like the mouse, except that its feet and claws seemed abnormally large and its whole body had an oddly deformed look to it. Sharon's hands trembled even more violently as she held it, as if her hands themselves sensed something wrong.

The white rat-if that indeed was what it was-was also stiff with the rigor of death, but there was one other difference between it and the mouse.

The fur on the rat's neck had been shaved away and there was a dark bruise, in the center of which was a puncture mark, as if a needle had been used to pierce the rat's skin.

Both the animals had small metal tags attached to their right ears. Sharon had to fish in her purse once more to find her reading glasses before she could make out the tiny letters stamped on each of the tags.

The tags were nearly identical. Each bore the same series of numbers and letters: 05-08-89/M#61F#46.

But on the tag on the rat there was an additional number: GH13.

Sharon stared at the creatures for a moment, trying to figure out what the numbers might mean. The first six digits, she was absolutely certain, were a date. But the rest?

And then she thought she knew the answer, but it didn't quite make sense.

Quickly returning the two small corpses to her purse, she put the car in gear and sped away, her mind already trying to figure out a way to confirm her suspicions.

Was it really possible, she wondered, that the two animals could have come from the same litter? And if they had, what had been done to the second creature that could have made it grow so large?

She shuddered, knowing already that she didn't want to know the answer-and at the same time knowing that nothing would stop her from finding out exactly what that answer was.

Mark closed his notebook as the three-ten bell rang and fished under his desk for his book bag. He hadn't taken much in the way of notes today; indeed, he'd found it hard to concentrate on the history class at all. Instead he'd found himself fidgeting and glancing at the clock every few minutes, waiting eagerly for the bell to ring. Now, as the last echoes of its shrill clanging died away, he was on his feet and out the door. He took the stairs to the main floor two at a time, then paused as he heard Linda Harris calling his name. She hurried up to him, her expression apologetic.

"I'm sorry about this morning," she told him. For the first time in nearly three weeks, she hadn't met him at the corner three blocks from the school so they could walk the rest of the way together. He'd waited a few minutes, then decided she wasn't coming at all. When he'd gotten to school he found that she was already there, sitting on the steps with Tiffany Welch. When he'd spoken to her, she pretended she didn't hear him for a minute, then been cool when she finally acknowledged his presence. "I-I guess I acted like a kid this morning, didn't I?" she asked now.

Mark shrugged. "I just don't see why you're so mad," he said.

Linda fell in beside him as he started toward the main doors. "I guess I'm not mad, really," she said. "I just…" She looked at him a moment, her brows knit into a frown, and decided not to utter the words hovering on the tip of her tongue. "Never mind," she said. "Where you going? Want to go get something to eat?"

Mark shook his head. "Can't. I have an appointment with Dr. Ames."

Suddenly the frown was back on Linda's brow. "How come?"

"He's just checking me over," Mark replied distractedly as his eyes scanned the crowd of students that filled the hallway. "Did you see Robb anywhere?"

Now Linda's expression grew bewildered. "Robb?" she asked. "I thought you and Robb had a fight yesterday!"

"We did." Mark grinned. "And I could have taken him, too, if your mom hadn't stopped us. Anyway, he's going out to the center, too. He said he'd meet me here."

Just then Robb came around the corner from the eastern wing and tossed his book bag to his sister. "Take it home for me?" he asked. Linda gave him a sour look.

"What if I don't?" she challenged.

"But you will," Robb teased. "You don't want to look like a brat in front of your boyfriend, do you?" He snickered as both Linda and Mark reddened, then delivered a light rabbit punch to Mark's upper arm. "Come on-Ames hates it if we're late."

Mark hesitated only a second, turning away before he saw the dark look that came into Linda's eyes. Following Robb, he trotted down the steps toward the rack where the other boy's bike was parked. As Robb got the bike moving, Mark jumped onto the rack on the back, feeling the metal tubing give slightly as it accepted his weight.

"Jesus Christ," Robb complained. "How much do you weigh?"

"Five pounds more than last week," Mark replied. "And it's all muscle, so you'd better watch out!"

Linda, standing at the top of the steps as she watched the two boys ride away from school, felt a strange mix of emotions. She supposed it was nice that Robb and Mark were becoming friends again, and she'd already decided that she couldn't expect Mark never to change, but still, there was a little voice inside her that kept telling her something was wrong, that Mark wasn't really changing at all.

Instead she had the weird feeling that hewasbeing changed, and that he didn't even know it. Disconsolately, she slung Robb's book bag over her arm and started home.

"There's my boy!" Marty Ames exclaimed as he strode into the examining room where Mark was stripped down to his underwear. A nurse had already checked his blood pressure and pulse, weighed him, measured him, and checked his lung capacity. "How're you feeling?"

"Great," Mark told him. "I'm up another couple of pounds, and I've grown almost half an inch."

Ames's brows arched appreciatively and he scanned the newest statistics the nurse had entered into Mark's computerized medical record. "Lungs up a few cc's, too," he commented. His eyes shifted to Mark. The bruises on his face had almost completely disappeared, and only a thin scar marked the spot where his forehead had been cut. "Any pain in your ribs?" Mark shook his head. "Well, in that case, I pronounce you healthy."

Mark's face registered his disappointment. "You mean that's it?" he asked uncertainly. "I'm done out here?"

"I didn't say that." Ames chuckled. "In fact, now's when the real work begins. The vitamins are all fine, but you still have to do most of the work. Pull on a pair of shorts and come with me."

Mark fished in his book bag for the gym shorts he'd started carrying with him the previous week, then put on his socks and tennis shoes. Leaving the rest of his clothes and the book bag where they were, he followed Ames out of the examining room and through the halls to the gym. He'd spent time here before, learning how each of the machines worked and how it acted on his muscles, but today Ames led him through a door into a smaller room where Robb Harris was already working out on a rowing machine, his eyes fixed on the screen that curved around in front of him.