NANCY STAGGERED BACK, almost losing her footing. This girl was out of control. Nancy would have to deal with her carefully.

"I'm telling you, you're mistaken," Nancy said. "I don't know you."

"Maybe not," the girl countered. "But I'm going to make sure you remember me for a long time."

The girl pulled her right hand back, as if to rake her nails across Nancy's face. As her arm started to move, Nancy reached up and caught her wrist. Her thumb pressed on a spot where the nerves that control the hand run close to the surface. The girl turned pale, and her hand opened.

"Let me go," she muttered through clenched teeth.

"Kim!" a high-pitched voice called. "What's going on in there?"

Nancy took a quick step to the left and put her back to the wall, ready to take on two attackers if she had to. But the newcomer was Sally, her hazel eyes filled with concern.

"Nothing," Nancy's opponent said, almost spitting out the word. A moment later she stormed out of the rest room.

"Who was that, and what is her problem?" Nancy asked Sally.

"Her name's Kim Forster," Sally replied. "When she saw you walk in with Victor, it kind of lit her fuse, if you know what I mean."

"You mean, she and Victor-" Nancy leaned back against the wall. "I thought maybe she found out I was investigating this case and she was involved somehow."

"I doubt it," said Sally. "She's got this intense thing for Victor. They dated for a while. Kim didn't seem that upset when it ended, but for the past couple of weeks all she can talk about is what a rat he is."

"That's odd," Nancy remarked. "I wonder what set her off?" With a shake of her head, she added, "Well, I've got other things to worry about. Have you discovered if any other kids have been approached by the grade-changer?"

"No luck so far. How about you?"

"Nothing yet," Nancy told her. "Listen, I'd better get back to Victor. He's probably wondering what happened to me."

"And I'd better get back to Kim," Sally replied. "Now that she's cooled off a little, I'd better make sure she stays that way."

As Nancy walked back to her table she could almost feel Kim's glare boring into her back. If that was the way Kim was after cooling off, it was a good thing that she hadn't stayed heated up!

Victor looked up as Nancy sat down. "You were gone so long that I went ahead and ordered for you. A cheeseburger and french fries-okay?"

"Fine. I just ran into a friend of yours." Nancy made a slight motion of her head in the direction of Sally and Kim's booth.

Victor glanced across the room, then shifted uneasily. "Oh. Did you have any, uh, problems?"

"Sort of. Kim seems to be pretty hot-tempered and impulsive."

"You could say that," he replied with an empty little laugh. "Did she try to show you her deed? The one that says she owns me?"

"No," Nancy said, chuckling.

"Good. It's a forgery, anyway." He paused and studied the top of the table. "We had a few dates, that's all. No big deal. And we stopped dating, because it wasn't working for either of us. We were both okay with that-I thought. But now she looks at me like I'm a worm she's planning to dissect for her biology project."

Nancy leaned back to let the waiter set their food on the table. She wanted to get off the topic of Kim and back to investigating the case. "How long have you been interested in computers?"

"Since I was fourteen," he said. "I was in a car accident. I got banged up pretty bad-missed a whole year of school. I should have graduated last year, but I had to make up the year I lost. Anyway, while I was laid up, I started hacking around with my dad's home PC. I couldn't do much else that year." Victor leaned back in his chair and smiled. "And that that is how I became the computer genius you see before you today." is how I became the computer genius you see before you today."

"I bet I can guess what you're going to study in college," said Nancy, taking a bite of her burger.

His smile disappeared, and he became serious. "The big question isn't what, it's where. The places that have really good Information Sciences programs cost a fortune. I don't have that kind of money. I'm at Brewster on a full scholarship. So either I get a college scholarship or I settle for a second- or third-rate school. That's where you come in."

"It is?" Nancy asked cautiously.

"For sure. You're going to help me raise my grades. I'm counting on it." He gave her another of his charming grins.

Nancy couldn't help smiling back, but as she did, she studied Victor's face. He seemed to be open and uncomplicated, but could she really tell? Did his remark have a double meaning, or was he simply talking about the tutoring program?

"How about a movie tonight?" Victor asked boldly as he wolfed down the last of the fries.

Time to tell him about Ned, said Nancy to herself. She told Victor all about her relationship with her boyfriend. To her surprise, Victor began searching for something under the table, then the chair. "What are you looking for?" she asked.

"Ned," he said with a smile.

"Well, he's sure not here." Nancy laughed.

"Exactly," said Victor, gazing meaningfully into her eyes. "I am. So let's forget about Ned."

"I can't," said Nancy. "Anyway, I'm your tutor-I don't think I can go out with students."

"It's not like you're a real teacher. Come on, why not?" Victor replied.

Nancy felt herself melt a little in the warmth of his gaze, but all she said was "I have a couple of errands to run. Let's get the check."

"I should get home, too," said Victor. "My computer must be starting to wonder what happened to me." He signaled the waiter and paid for their burgers, and then they left.

As she drove home, Nancy reviewed the case. Even though she liked him, Victor Paredes definitely had to be a suspect. He had bragged to her that he could do whatever he wanted with the computer system. He hadn't made a secret of his poor grades in English or about his need for money to go to college. What if he had first cracked the school records access code while trying to change his own transcript, then realized that he had a very profitable product to sell? He was no dope-he might have decided to leave his own grades unchanged for the time being, just in case suspicion fell on him. Hadn't he been awfully quick to bring up just that point?

Nancy laughed. That was like saying that because a criminal might try to look innocent, anyone who looked innocent must be guilty!

Pushing Victor out of her thoughts for the moment, Nancy started to think about Kim. Had her attack on Nancy really been caused by jealousy? Or was she somehow connected to the case? But Nancy didn't see how Kim would know that she was a detective, or that there was a grade-changing scheme.

And what about Randi, the newspaper reporter? Was she as straight as she seemed? She obviously knew how to use the computer very well, and she had seemed anxious to clear her computer screen when Nancy showed up. In addition, she was pet.i.te and a brunette, just as Mrs. Tillman had described I. Wynn. So far, she was the only one who fit that description.

And, of course, there was Phyllis Hathaway. She was still Nancy's number-one suspect. Nancy resolved to find out more about her and her mysterious friend Dana the next day.

The next morning Nancy had a break after her third student. It wasn't long enough to do any investigating, but it did give her time to go to the faculty lounge and fix herself a cup of tea. As she was carrying it back to the learning lab, she ran into Victor. He was standing in the hall talking to a heavyset young woman with curly dark hair and green eyes. She was wearing a navy blue business suit and had a still-damp raincoat draped over her arm. It had poured all morning.

"Hey, Nancy," Victor called. "Come here, I want you to meet someone." When Nancy joined them, he continued, "You were asking questions about the school computer system? Here's someone who knows it inside out. Meet Ms. MacCauley, president of PointTech Computers and queen of the River Heights hackers."

"Victor!" the woman said in mock outrage. "I've told you before, you don't call people hackers these days. It's like-oh, I don't know what, but don't do it."

Victor saluted. "Yes, ma'am!" Then he turned back to Nancy. "Ms. MacCauley heads up PointTech, the company that designed the system here at Brewster. Whenever it goes down, she's the one who catches the flak and puts it back on line."

"Does the system go down often?" asked Nancy.

"No," Ms. MacCauley answered.

"Yes," said Victor at the same moment.

"Let's put it this way," Ms. MacCauley said, smiling. "It's a complex system that's had a lot of different demands put on it. It's designed to handle them, but sometimes the pressure makes it a little ornery. That's when I step in, to give it lots of strokes and a few well-placed strategic kicks."

Nancy returned the woman's smile. "I can easily imagine kicking a computer," said Nancy. "But how do you go about stroking it?" Maybe this was her chance to learn something helpful about the computer system at Brewster. "Do you have a few minutes to show me a little more about the system?"

Ms. MacCauley glanced at her wrist.w.a.tch, then said, "I guess I do."

"There's a terminal in the learning lab, where I'm working," Nancy added.

Victor gave a snort and said, "Thanks to Ms. MacCauley, there's a terminal in practically every s.p.a.ce in this school, except the broom closet!"

The woman turned to him and said with a straight face, "What happened to that one? Did someone steal it?" Then, laughing, they all went up to the learning lab.

A few moments later Nancy found herself seated at the terminal with an expert leaning over each of her shoulders. She turned on the power, typed in her pa.s.sword at the log-on prompt, and hit the Enter b.u.t.ton.

A list of menus appeared on the screen. "Is there anything in particular you'd like to know how to do?" Ms. MacCauley asked her.

Nancy hesitated a moment. She had to be careful what she asked. If Victor was the grade-changer, she didn't want him to suspect she was on his trail.

"I was wondering," she said lightly, "if someone sent you a message, would there be any way of finding out what terminal it came from?"

"You could," Ms. MacCauley replied with a nod. "If you refuse the message, the computer will tell you that it's returning the message to its place of origin. It will say: 'Returning refused message to terminal twelve,' or whatever terminal it is."

"And how could you find out where terminal twelve is located?" asked Nancy.

"You couldn't," Ms. MacCauley replied. "You'd have to have access to a set of computer files that the regular student user couldn't get to."

She'd have to ask Walter to look at the file, thought Nancy. "Why can't students have that information?" she asked Ms. MacCauley. "Is it for security reasons?"

"Not really. We simply didn't want to overload the active systems with files students don't need. By storing this information in a separate reference directory, we freed up some s.p.a.ce for active use. No one but authorized personnel can get into that file."

"Authorized personnel and me," Victor piped up.

Ms. MacCauley shot him an exasperated look. "Victor," she said, covering her ears, "I'm not hearing this. Don't tell me these things."

Disregarding the playful warning, Victor leaned in closer to Nancy-closer than he had to. "Watch this," he said as his fingers flew across the keyboard. "Ta da!" he crowed finally.

There it was! A complete listing of all the terminals in the school next to their code reference numbers. Nancy's heart skipped a beat. Maybe she could just get a copy of the list now without bothering the headmaster. But she couldn't ask for it without making Victor suspicious.

"Oh, no!" Nancy exclaimed suddenly, glancing at her watch. "A student's due to arrive any minute, and I'm not prepared yet!"

Nancy jumped up from her seat and pretended to twist her ankle. She pitched forward, bringing her hand down on the keyboard-making sure to hit only one b.u.t.ton: Print Screen.

Noisily, the printer sprang into action. "Oh, my gosh!" she cried, feigning surprise.

"Are you okay?" asked Victor.

"It's just my ankle," she moaned. "I hope it doesn't swell up."

"I'm going to get a cold, wet towel," Ms. MacCauley volunteered. "That might keep it from swelling."

"Let's take a look at that," said Victor as Ms. MacCauley left the room. He knelt down in front of her and propped her foot up on his leg. Slipping off her loafer, he gently rotated the ankle. "Does that hurt?" he asked, his amber eyes meeting hers.

They were startled by a strangled cry from the doorway. Nancy looked over and saw Kim standing there, her face crimson with anger.

"You'll be sorry," she cried. "You two will wish you were never born when I'm through with you!"

Chapter Six.

KIM TURNED AND FLED down the hall.

"I'd better try to talk to her," Victor said, dashing out of the room.

Nancy hit the Advance b.u.t.ton on the printer, and the paper moved up enough so that she could tear off the three sheets of the printout and slip them into her bag.

"What was that about?" a voice spoke up behind her.

Nancy whirled around to find Ms. MacCauley standing in the doorway. For a moment she thought the woman had been talking about the printout. Then Nancy realized she was watching Kim and Victor.

"Just some kind of misunderstanding," said Nancy.

Ms. MacCauley turned her attention back to Nancy. "How's your ankle?" she asked, offering her a few cool, wet paper towels.

"Huh-oh, it'll be okay." Nancy took the towel and pressed it to her ankle. "Do you know what else? I feel so stupid. My student isn't even due to arrive for another half-hour. I was mistaken. I'm not used to my schedule yet."

"Terrific," said Ms. MacCauley, settling herself at the terminal. "We can continue while Victor sorts out his love life." With nimble fingers, she closed out the directory of computer terminals. She chuckled and shook her head as she worked. "That Victor! He'd better watch his step or he'll land in big trouble someday. Once you know how to break into a system it's very tempting to make mischief. Believe me, I know."

There was something in the way she said "I know" that jolted Nancy's memory. Nancy gave Ms. MacCauley a probing look. She was obviously in her early twenties, only a few years older than Nancy. Nancy tried to remember what her father had told her about the girl who had gotten in trouble for using her computer to alter her parents' telephone bills. Ms. MacCauley seemed to be about the right age. She had her own computer company in River Heights, too. And the remark she'd just made indicated that she had gotten into computer-related trouble. Nancy would be willing to bet that Ms. MacCauley was the girl her father had defended!

Trying to remain calm, Nancy said, "I suppose a person could tamper with all sorts of things, like bank records, government files-even telephone bills."

Ms. MacCauley looked so sharply at Nancy that Nancy knew her hunch was right.

"Well, uh, let me show you how the E-mail works," Ms. MacCauley said, her attention on the computer once again. "See these menus on the screen?" Nancy nodded, and Ms. MacCauley went on, "You see the word MAIL? That allows you to send and receive electronic mail. Do you have a mailbox yet?"

"Phyllis Hathaway gave me a pa.s.sword," Nancy replied. "But I don't know if I have an E-mail box."

"That's easily fixed," said Ms. MacCauley. She tapped in some commands. "There. From now on, whenever you log onto the system, it will tell you if there's any E-mail in your box. I've just sent you today's student mailings. Try it. Log off, then log back on."