In math the next morning, Mr. Langel stood in front of the board, telling the class how to calcu- late a rectangle's area. He started doing an impression of the Count from Sesame Street. "One! Ha-ha-ha!" he declared, smiling.

But Olivia couldn't roll her eyes as she usually did at Mr. Langel's sense of humor. Could he be a vampire? she wondered, looking at him suspi- ciously. After all, his hairline descended into what her mom called a widow's peak--a point in the center of his forehead--which made him look vaguely vampiric. Olivia wondered what color his eyes really were. She pictured him climbing out of a coffin earlier that morning, pajamas still on.

Then she realized that if her goofy math teacher could be a vampire, anyone could! She turned her attention to a stocky Goth boy with an earring and spiky hair sitting at a nearby desk. His hand rested next to his notebook, and there was a leering skull-and-crossbones ring on his pinky. Now that she thought about it, Olivia realized that she'd never seen him open his mouth. Was it because he hadn't had his fangs filed?

She could deal with her sister being a vampire, because she knew Ivy would never do anything to hurt her. It was all the other vampires at Franklin Grove Middle School that Olivia was suddenly worried about. She surreptitiously counted the number of other students in the class: twenty-one possible vampires. She pulled her cardigan more tightly around herself.

What about the cheerleaders? she wondered. Nobody said a vampire couldn't wear pink. Besides, if anyone had some evil in her, it was Charlotte Brown. Now I'm being ridiculous, Olivia told herself. No way is Charlotte cool enough to be a vampire!

She looked down at her blank paper and wrote, "VAMPIRES DO NOT EAT BUNNIES" ten times without stopping. It sort of helped, except that, when she was done, she realized she'd missed out on how to calculate the area of a trapezoid.

By the end of class, Olivia was obsessing about the ball planning meeting after school. Everyone was nice to Ivy, but what if they discovered she was an impostor? What if they found out that she knew their secret? Ivy had said there could be trouble. . . .

Quickly Olivia tried to think of some sort of protection she could take with her, just in case. She had a nearly empty nail polish bottle in her purse. She thought maybe she could empty it and then fill it with holy water. But, then, what if that was a myth, too? And where was she going to get holy water, anyway? Would a pencil count as a stake? she asked herself. She did have two of those in her purse. Garlic! she thought suddenly. At least she knew that wasn't a myth.

At lunch, Olivia was hoping for a garlic- infused daily special, but no luck. The specials board announced that today it was crab salad, and as Olivia read it something clicked inside her head. I get it! she thought. Vampires are just differ- ent kinds of humans, just like crabs and lobsters are different kinds of crustaceans! They're pretty much the same thing: one big happy crustacean family! And from then on, Olivia felt much better.

She smiled at everybody she saw for the rest of the afternoon, right up to when she grinned goofily at Ivy at the beginning of science.

"How are you?" Ivy asked in a low voice.

"Great!" Olivia said brightly. "It's like you're a lobster!"

Ivy clearly didn't get it, but she didn't press. "Are you still up for the planning meeting this afternoon?" she whispered.

"For sure," Olivia said. "I can totally handle the vamp--" Ivy's eyes widened. Olivia coughed and lowered her voice. "The meeting," she said instead.

At the end of class, Olivia followed her sister into the girls' bathroom.

After they'd switched clothes, Ivy stood looking in the mirror. "Now I wish I didn't have a reflec- tion," she said, pulling Olivia's pink gym shirt away from her chest. Then she leaned forward with an eyeliner pencil to do Olivia's eyes. "Remember what you said about cherry punch at the meeting?"

"Uh-huh?" Olivia said.

"Myth," Ivy said simply. "Vampires don't just eat meat and drink blood. You can eat the crack- ers or chips or whatever's there."

"Okay," said Olivia, feeling just a little less nervous.

"Is there anything else you need to know?" Ivy asked.

Questions raced to the front of Olivia's mind and raised their hands eagerly. Finally, she picked one. "Are all Goths vampires?"

"In Franklin Grove? Not all but most," Ivy told her.

"What about everybody else?"

"Bunnies, like you," Ivy answered matter-of- factly.

"Are you immortal?" Olivia asked.

"That's a tough one." Ivy put Olivia's bag down. "Not really. But I might get to see the day people live on Mars."

"What can kill you?" Olivia wanted to know.

"What can kill you?" Ivy countered. "Listen, Olivia, vampires are people, too."

Olivia nodded. "I know. Like you're a lobster and I'm a crab," she said automatically. "But we're both crustaceans."

"No," Ivy said. "I didn't say we were seafood. I said we were people. With hearts and souls and everything. We're into life, liberty, and the pursuit of happiness just like everyone else.We don't even talk about it among ourselves that much. It's like you being a vegetarian. That's not such an enor- mous deal, right?"

"Right," Olivia admitted. Totally. No biggie. "Thanks, Ivy." Olivia scrunched up her nose. "I guess this vampire thing does take some getting used to."

Ivy assumed a vacant look. "Really?" she squealed in her cheerleader voice.

Even though she knew she had nothing to fear, the hair on the back of Olivia's neck stood on end the moment she and Sophia came in sight of the towering FoodMart sign. Sophia was talking excitedly about the ball as they walked, but Ivy's words were the only ones Olivia could hear: "I go to BloodMart like everyone else. There's one in the basement of FoodMart."

Olivia imagined a huge, dim underground crypt, filled with enormous vats of swirling red liquid. Spigots dripped gruesomely, and blood- soaked napkins littered the floor. Before she knew it, she and Sophia were walking through the store doors and it was too late to flee.

As they walked down aisle nine, questions flooded Olivia's mind. How much blood would be needed to satisfy every vampire in Franklin Grove? How many vampires were there in Franklin Grove, anyway? Dozens? Hundreds? Thousands?

She and Sophia came upon the same nose- ringed stock boy with the midnight stubble.

Maybe that wasn't cranberry juice he was stacking after all! Olivia thought. Her heart raced. He must be a vampire since he opens the door.What if he can smell my fear? She put her hand to her neck and started hyperventilating.

Sophia gave her a weird look. "You're breath- ing like a horse," she said. Then she turned to the stock boy and said, "Pumpernickel." He obedi-ently unlocked the staff door, and Olivia scurried past him, trying to avoid eye contact.

The dark staircase creaked with every step. Olivia thought she heard laughter, then creatures scurrying in the walls, then the sound of liquid running ominously in pipes. She was scared of tripping and tumbling down the stairs, but she was even more scared of placing a hand on the wall to steady herself. What if it was damp?

At last they reached the narrow hallway at the bottom. Olivia trailed farther and farther behind, terror making Ivy's boots feel even heavier than usual. She passed the first mysterious unmarked door. It was huge and made of dark, brushed metal. It also had a slot to look through so that those inside could see who was outside wanting to come in. The shutter over the slot was closed, but Olivia could hear talking and laughing from a crowd inside.

BloodMart! Olivia thought. On the other side of that door, vampires are thirstily drinking BLOOD!

She lurched forward, feeling sick. She put her hands on her knees. Ivy's black fishnet stockings crawled like spiders beneath her fingers.

"Will you come on?" Sophia called from up ahead.

Olivia thought if she tried to stand up again right now she'd puke.

Sophia's footsteps came closer. "Ivy, relax," she said. "I know you have cold feet about being head of decorations, but it's just a meeting. Besides, you're already doing a killer job."

Then she grabbed Olivia's hand and dragged her to the door at the end of the hall.

The vampires were waiting within: Vera, with her startling shock of white hair, Raymond, with his fiendishly bald head, Anise, as gaunt and hol- low eyed as an ex-lover of Count Vira.The Beasts, looking more bloodthirsty and beastly than ever.

Melissa, with her officious manner and disarm- ingly chunky glasses, offered Olivia some punch. Olivia declined. "Oatmeal raisin cookie?" Melissa tried. Olivia shook her head like a zombie.

Now all the vampires were taking their places around the sacrificial slab of a table.

"May the Secret be cloaked in darkness," Melissa intoned solemnly.

"And never see light of day," came the response.

Olivia collapsed into her seat.

"Okay, people," Melissa began, flipping through her notes. "First item on the agenda is decorations. Ivy?"

Olivia couldn't speak. All the vampires were looking at her with their contact-lens-covered eyes.

"Ivy?" Melissa said again.

Sophia pinched her hard, and Olivia jumped. She reached into Ivy's black velvet messenger bag and pulled out her white All Hallows' Ball-- Decorations folder.

The papers rustled in Olivia's trembling hand. "Take one and pass them on," she whispered.

Olivia stumbled through her presentation. She'd organized her ideas into two categories: "Big Things," which included stuff like the cen- terpieces--fake tombstones featuring celebrity vampires' names, surrounded by bouquets of white lilies--and "Little Things," which included random stuff like rubber spiders, bats, cobwebs, flaming torches, and so on.

Even through her haze, Olivia could tell that the committee, in its Goth way, was pleased. Almost against her will, she started feeling better.

Oh, my gosh, she thought nervously, I might actually make it through this meeting without losing my mind, being bitten by a vampire, or driving a stake through anyone's heart!

She'd saved the best idea for last: a bunch of old vampire movie posters she'd found on eBay.

"That sucks!" Anise declared, and everyone nodded. Olivia smiled in spite of herself.

One of the Beasts cleared his throat. "I have an idea," he said, a devilish grin spreading across his face.

Olivia's pulse quickened.

He held up a long, pale finger. "A decoration that's cheap and plentiful."

"Let's hear it," Melissa invited reluctantly.

"Something better than posters." The Beast leered at Olivia. "How about we round up a bunch of dead bunnies from the morgue and line the walls with them?"

The other Beasts burst into laughter.

Olivia's stomach churned.

Melissa seethed. "You guys are disgusting!"

Raymond balled up his list and chucked it at the boy.

I have to get out of here! Olivia thought. She leaped up from her chair, blurted, "Sorry" to Sophia, and bolted out of the room.

She raced down the narrow hallway, its walls closing in around her. On the stairs, she tripped and skinned her knee, but she just scrambled to her feet and kept running.

She burst out through the doors of FoodMart and finally slowed to a stop. She leaned against the outside of the building, taking deep breaths of fresh air.

A few seconds later, Olivia heard someone coming up behind her. She spun around, ready to fight for her life, but it was just Sophia.

"What's wrong with you?" Ivy's friend asked.

Olivia didn't answer. She was breathing too hard.

Sophia shook her head and said, "You've been acting strange all afternoon. It's one thing for Ivy Vega to be out of her element at social functions, but my best friend has never in her life fled from a room." She stepped closer and peered into Olivia's eyes.

Olivia looked away.

Sophia said, "What's going on?"

"Nothing!" Olivia gulped.

"What is going on?" Sophia repeated more forcefully.

"Everything's totally fine!" Olivia squealed hysterically.

Sophia narrowed her eyes.

I just said "totally, thought Olivia."

"Did you just say `totally'?" demanded Sophia.

Olivia sank down on the curb. It was obvious that Sophia knew something weird was going on. She was going to have to confess. "I'm not Ivy," she muttered in defeat.

"What?" said Sophia.

"I'm Olivia Abbott."

Sophia grabbed Olivia's arm. "What have you done with my best friend?" she demanded anx- iously.

"Nothing!" Olivia snapped, twisting out of her grasp. "She's at cheerleading practice," she admitted.

Sophia was speechless for a moment. Then she sat down beside Olivia on the curb. "I'm listen- ing," she said.

It took a long time to tell the whole story: dis- covering they were twins, switching identities, Charlotte Brown, Ivy's date with Brendan, the ball. In the middle of it all, Sophia was nice enough to go inside and buy Olivia some aspirin and a Diet Coke.

After getting over her initial shock that Ivy had a twin sister, Sophia seemed to take the news surprisingly well--except that Olivia left the most awkward part for last.

"And then yesterday," Olivia said slowly, "Ivy told me what kind of person she is."

"What do you mean?" Sophia asked inno- cently.

"What kind of people you all are."

Sophia looked thoughtful for a second. "Goths?"

"No, the really secret thing," Olivia said mean- ingfully.

"Oh!" Sophia's eyes opened wide. "She told you that?"

"Yup," Olivia said guiltily. "I wasn't supposed to tell anyone. She said we could both get into big trouble."

"She never should have told you," Sophia said firmly.

"She didn't have a choice," Olivia responded. She shut her eyes and let out a heavy sigh. "This is all my fault." She thought she was going to start crying, but then she felt Sophia's hand on her shoulder.

"Don't worry," Sophia said quietly. "I won't tell anyone."

"Really?" Olivia said, opening her eyes.

"Really," Sophia said sincerely. "Ivy's my best friend."

"And you're not mad?" Olivia asked.

"A little," Sophia admitted with a shrug. "Ivy could have told me she'd found her long-lost twin sister. I feel like I've been missing all the fun. But at least this explains why Ivy was suddenly so good at party planning!" She peered at Olivia's face. "You really had me fooled. I mean, I didn't notice any resemblance between you and Ivy at all."

Olivia smiled. "That spray-on pale stuff does wonders."

Sophia laughed and stood up. "Come on," she said.

"Where are we going?" Olivia asked, getting to her feet.

"Cheerleading practice," Sophia replied. "If Ivy's hopping around like a bunny, I need to see it!"