"Liz? I thought you were upstairs."

"I'm at the mall, Jess. Please don't be mad, but I remembered something vitally important I had to do."

Jessica drummed her fingers impatiently on the counter as she listened. "You're at the mall? I'm not mad, Liz, but you're supposed to be up in your room resting for the party."

"I'll be home soon, I promise!"

"How soon, Liz? There's a lot of work to be done before the kids get here." The fingers were still drumming.

"Not to worry, Jess. I'll be there in a flash. Why don't you start things?" And the line went dead.

"Well, how do you like that? She wants me to start the work!"

Four.

Jessica kept telling herself she shouldn't be upset with Elizabeth. After all, she thought, Elizabeth was just getting back on her feet. So, OK, she had left her with all the work of setting up for the party. "Listen, Jessica Wakefield," she lectured herself, "haven't you ever ducked out on work and left Elizabeth to do it?" She sighed and got out the onion soup mix to make the dip.

Actually, that was just the trouble. Normally it would have been Jessica calling from the mall to say she'd be late and for Elizabeth to go ahead setting things up without her. This just was not like Elizabeth.

"Now, don't start creating a humungous, imaginary crisis over nothing," she cautioned herself aloud. "Knowing my sister, she might even be picking up some wonderful surprise for the party."

Still, it nagged at her.

"Stop it," Jessica commanded herself. "If you don't make that dip, the kids will have to eat powdered soup mix." She giggled and kept working.

Jessica checked the pool, skimming out leaves and twigs, and made sure the chlorine level was right. She set out the chips and dip and lugged the ice chest filled with soda out onto the patio. Then she moved the stereo speakers.

Pausing to look in a mirror, she reacted with horror. "Yaaaaagh," she gagged, looking at her tangled hair and red, sweaty face.

That was the problem with doing all the work. You wound up red-faced, sweaty, cross, and tired. Jessica made one last circuit of the patio, going around the pool to check the little wrought-iron tables, and then raced inside to take a shower.

"Hey!" she yelled in surprise when she got upstairs. She heard the sound of the shower running. "Is that you, Liz?"

"In a minute," she heard floating out from the volcano of steam and froth in the shower.

"Well, how do you like that?" Jessica muttered. Elizabeth had come home, done nothing to help, and sailed into the shower first!

"Elizabeth Wakefield, you come out of there!" Jessica raged.

"What?" said Elizabeth, turning off the shower, wrapping a towel around herself, then jumping out and smiling radiantly at Jessica. "Isn't this going to be a great party?"

Jessica stood there glaring, but Elizabeth didn't seem to notice. She just skipped past and darted into her room, looking back out to say, "Hey, Jess, you'd better get a move on. You're an absolute mess."

Jessica threw up her hands, got undressed, then went into the shower.

By the time Jessica put on her ice-blue bikini for the pool party, Elizabeth was already out of her room.

"Liz," Jessica called out. "You there?" No answer.

Jessica checked herself out in the mirror, examining her slim, perfectly tanned figure and her smashingly daring bikini. She smiled. "Not bad," she murmured. The boys of Sweet Valley wouldn't have a chance that night.

By the time she came downstairs, the gang was already starting to arrive. Gathered around the pool were Cara Walker, Lila Fowler, and Enid Rollins, Todd Wilkins and Ken Matthews, the football captain, John Pfeifer from The Oracle, and even crazy Winston Egbert with his new girlfriend, Mandy Farmer. They were all standing around somebody near the diving board, somebody who had their undivided attention.

Jessica heard a provocative, flirtatious laugh rise from the circle of boys. "That's my laugh," she whispered, confused. But it was Elizabeth doing the laughing.

Jessica strolled over for a closer look, and her eyes almost popped out. It was Elizabeth, all right, but she wasn't wearing her old swimsuit. She looked simply sensational in a brand-new, very revealing green bikini. It sure wasn't Elizabeth's usual style.

It wasn't only the new bikini, which Elizabeth had bought at the mall while Jessica slaved away like Cinderella. No, it was something in the way Elizabeth moved among the awed guys. She was holding a platter of chips and dip, and as she turned between Ken Matthews and John Pfeifer, she treated each of them to dazzling smiles.

Jessica sensed someone standing beside her, and looking around, saw it was Todd. He was gazing at Elizabeth with an odd expression on his face. He looked at Jessica. She looked at him. They glanced back toward Elizabeth.

"Well, I guess she's feeling better," Todd said with an effort, looking for something positive in this strange behavior.

"If she felt any better, she'd be orbiting the moon," muttered Jessica.

But Jessica couldn't really complain. She was glad to see Elizabeth enjoying herself so much. The party was a blazing success, largely because of Elizabeth's radiant performance. She picked out the music, insisted on dancing with every boy, and kept up a nonstop chatter that the guys found fascinating.

Jessica and Todd stood by the patio doors drinking sodas and watching the new firefly of the Wakefield family.

Todd sighed. "It's terrific to see her so happy," he said, though his hopes of being alone with Elizabeth were rapidly disappearing.

"Yeah. She's so happy she doesn't notice we're out of chips, ice cubes, and soda," Jessica said.

It was weird. At parties Jessica was always the one who whirled and sparkled while Elizabeth kept the food coming. Now Jessica was doing all the work.

Just then Winston Egbert came up. "Kind princess, something to wet my parched throat before I expire, please! And a drink for my lady."

Jessica felt a curious twinge of jealousy. She knew Winston had been crazy about her since grade school, and usually she couldn't be bothered with him. But tonight was different. He was just about the only boy at the party not hanging all over Elizabeth. There was only one problem. He wasn't paying attention to anyone except Mandy.

"Hang in there, Win. I'll get more soda for you and Mandy," Jessica said, heading back toward the house.

When Jessica returned, she spotted Elizabeth standing in front of Ken Matthews, gazing soulfully into his eyes, as though hypnotized by whatever magic words he was saying. When she got close enough, she heard their conversation with amazement.

"I was just telling my father the other day, Ken Matthews knows all there is to know about football."

"Well..." Ken blushed.

"Oh, yes, you do, Ken. Why, I bet we'll see you out there playing with the Rams in a few years."

Jessica stood there, holding the tray of soda cans. Elizabeth Wakefield playing up to Ken Matthews? Impossible! She's just being friendly, just being a good hostess, Jessica told herself. So what if she's having more fun than I am? She deserves it. Jessica put the tray on a table and walked over to where Todd was sitting alone.

"Jess, have you been watching Liz?" he said cautiously. "Does she seem different to you?"

"What? No," said Jessica. "She seems really terrific tonight."

"Yeah, terrific with everybody but me."

"You're jealous!" she accused. "And you're mad because she's having a fantastic time, and the two of us are just-"

"Yes, Jess, the two of us. It occurs to me that you're just a little miffed at your sister for stealing your usual place in the spotlight."

"Todd, really, you can be an awful nerd sometimes," she said and stalked away.

Todd was wrong, she told herself. She wasn't the sort of person who always had to be the center of attention, was she? And neither was Elizabeth-at least not before that night.

Things began adding up in a way Jessica didn't like. But there it was. Elizabeth had conveniently gone shopping at the mall instead of being home to help with the party preparations. The Elizabeth Jessica had always known would never have done that. Elizabeth had told her she had something vitally important to do at the mall. And what was that? Buying a new bikini! Not only had she gotten out of setting up for the party, but she'd also sneaked home and into the shower right under her sister's nose. And finally, there was Elizabeth, looking sensational, flirting madly with every guy at the party.

Why, she's doing at least a hundred and thirty-seven things that I usually do, Jessica raged inwardly. At least, things I sometimes do. Once in a while.

She was so busy thinking that she might actually have walked blindly into the pool if she hadn't bumped into Cara Walker.

Cara turned, saw the tray of sodas Jessica was carrying, and took a can.

"Well," said Cara, looking over her shoulder toward the other end of the swimming pool, where Elizabeth was surrounded by five guys, "would you check out Miss Butterfly of the Year?"

"What kind of a crack is that?" Jessica snapped. "Isn't my sister allowed to have a good time?"

Cara apologized quickly. "I'm sorry, Jess. I didn't mean anything by it. It's just that I've watched you in action with guys and-"

"What?"

Cara's face turned beet red. Her apology was only making things worse, and she knew Jessica was getting mad at her. "Jess, you always know the right thing to do around guys. You're really terrific in everything, especially cheerleading, and you're a marvelous dancer, and you-"

"Calm down, Cara," Jessica said, then sighed. Usually she liked Cara telling her how terrific she was, but tonight she had other things on her mind.

"What I was trying to say was that I've never seen Liz in action. She's always friendly, but not this friendly. I thought she only had eyes for Todd, but tonight she's breaking all records for flirting."

Jessica hardly knew what to say, she was so angry. "My sister is not a flirt!"

"OK, OK. But she certainly seems different."

"She is not," Jessica snapped angrily. "She's been under a lot of tension lately, but she is not different. She's exactly the same."

Jessica walked away from Cara, trying to convince herself that what she had said was the truth. But she was afraid it wasn't.

Cara Walker had unwittingly suggested what was bothering Jessica most. She had been circling around it all evening, feeling it, but unwilling to say or even think it.

Elizabeth had somehow turned into her, Jessica! She was even out-Jessica-ing her. It couldn't happen. It must not be allowed to happen.

If she's Jessica, she agonized, then who am I?

She chased the confusing thoughts out of her mind by hurrying around and taking care of the party. She became a demon at work, getting ice cubes, cleaning tables, mopping spilled sodas. Keeping busy helped a lot. Still, every time she passed Elizabeth, she was startled all over again to see the lively, glowing face of her sister lighting up the party.

By the end of the party, everyone was looking at Jessica and Elizabeth and whispering. Everyone knew something was wrong.

Everyone, that is, except Elizabeth. She chattered on brilliantly and unknowingly until the last.

What seemed to Jessica like a million years later, the party finally ended. When the last person had left, she closed the front door and turned to her sister. "Liz," she said. "I want to talk to you."

Elizabeth's eyes fluttered. "Jessie, is my face flushed?"

"What?"

"I guess it's nothing. I seem to have the most horrible headache coming on."

Jessica felt alarm growing inside her. She wondered if Elizabeth was having a relapse. "What's the matter, Lizzie?" she asked quickly.

"It's probably nothing. I just feel a little woozy."

"Oh, please, go lie down," said Jessica.

"Well, maybe I'd better-if you don't mind," said Elizabeth, and the next moment she shot up the stairs two at a time.

Jessica hurried around the pool and the patio, cleaning things up. I hope she's all right, she thought.

It wasn't until she was almost finished that Jessica realized she had done all the work for the party. She had set up, dashed around like a servant all evening, and then cleaned everything afterward.

The only thing Elizabeth had done was decide to have the party.

Stop it, she told herself. Elizabeth would have done the same thing for her. She was just tired.

Sure, said another inner voice. She was really a decrepit wreck when she hopped up the stairs like a little rabbit about two seconds after saying she had a splitting headache. Every time there'd been work to do that day, Elizabeth had developed a sudden problem.

Jessica understood all these tricks well enough because she had used every one of them time and again on her sister.

And then she froze. The same frightening sensation swept through her. "Is it possible? Has Elizabeth turned into me?"

Five.

Jessica let herself in through the back door, relieved to be home. It had been one crazy day-all of it bad. She'd be lucky to get a decent grade on her English test, but that wasn't what was really upsetting her. Being unprepared for a test was not unusual for her. But it was for Elizabeth, and Jessica was sure her sister hadn't cracked a book all week.

"How could she have time for studying when she's on the phone with guys most of the time?" she asked herself aloud. "Then of course there has to be time for manicures, pedicures, doing her hair-" She stopped herself in midsentence and glanced around the empty kitchen.

"I'm talking to myself," she said in amazement. "I'm coming so unglued that I am actually talking to myself." She poured a tall glass of orange juice. "What I should be doing is talking to somebody else about Liz. But who?"

Todd? No, he was still at basketball practice. Their parents? They hadn't seen Elizabeth in action at the pool party the week before, and besides, Jessica didn't want to worry them.