Ten minutes into last period, as Mr. Strain was going over the procedure for the cheek-cell experiment, Ivy glanced down at the piece of paper that she and Olivia had been passing back and forth since the beginning of class. It had started when Ivy had jotted down one possible theory concerning their parents. Olivia's latest pink-ink-penned theory was about halfway down.

THEORY 14: Mom bites Dad, feels guilty, runs off with kids, can't hack single parenthood??? Ivy tapped her pen thoughtfully against her lips. Glancing up, she caught Vera shooting her a mean look. Ivy returned her stare, and Vera angrily whispered the word "traitor" right at her. Ivy rolled her eyes and scribbled, Vera should go eat some garlic!

Olivia smiled when she read it, looked in Vera's direction, and then wrote, Just ignore her!

Mr. Strain came around to hand out materials, and Ivy covered the page with her book so he wouldn't see it. "I read the article in today's Scribe," he said with a smile as he held out a tongue depressor for their experiment. "As twins, your cells should be nearly identical."

If so, then Olivia must have some vamp in her, thought Ivy. "Here's hoping," she said aloud.

"I keep meaning to ask," Olivia whispered once their teacher had moved on, "what are you doing this Saturday? My mom wants you to come over for lunch."

"Okay," Ivy said as she filled out their lab sheet.

Olivia sighed. "Then she wants to take the two of us shopping."

Ivy stopped writing. "I think that's the first time I've ever heard you sound unhappy about shopping," she pointed out.

"My mom is going completely overboard," Olivia explained. "After you left last night, she started researching Goth cookbooks, and got excited about some recipes she found."

"Really?" Ivy grinned. "Like what?"

"Blackberry blood souffle," Olivia said, looking like just thinking about it made her want to puke. "That does sound delicious," Ivy admitted.

"Gross," Olivia said under her breath.

"I hope that you will all discover something about your own genetics today," Mr. Strain told the class. "You may now begin."

As Olivia scraped the inside of her cheek, Ivy twirled her emerald ring around its chain. Their matching rings were the only things either of them had from their biological parents. While Olivia got to work on making their slide, Ivy took the chain from around her neck, and examined the ring thoughtfully. The emerald, a rich green, was set in a platinum band, which was covered with etchings in yellow gold that looked like rivers on Earth as seen from outer space.

As Olivia delicately pressed the two glass slides together, her ring sparkled up at Ivy.

Maybe the rings are some sort of clue, Ivy thought. Ivy pulled the microscope over and slid her ring under the lens. Bringing it into focus, she followed the etchings with her eye, turning the ring slowly.Maybe she'd find something written there, between the tiny rivers.

Something caught her eye as she rotated the ring, but it wasn't on the band. It was actually in the emerald: a tiny blurry shape that looked like it was floating in the field of bright green.

"What is it?" Olivia whispered. "Let me see!"

"I don't know," Ivy said softly. "Probably just a flaw in the stone." She kept trying to adjust the position of the ring and the microscope's focus, but she couldn't make the blob out clearly.

Her sister poked her impatiently. Ivy pulled the ring out from under the microscope and held it up. She squinted, trying to see whatever it was with her naked eye, but she couldn't.

She turned the ring over. When she brought it right up to her nose, she could just barely make something out. She brushed one finger lightly over the exposed underside of the stone and felt tiny marks.

There's something carved on the bottom of the emerald! Ivy realized.

"What do you see?" Olivia asked eagerly.

Without answering, Ivy quickly put the ring back under the microscope lens, upside down this time. She turned the knob to refocus the microscope until . . .

She could see a tiny symbol, clear as night: it was the shape of an eye, with a V inside it.

"I can tell that you see something!" Olivia whispered urgently. Shoving Ivy over, she held her ponytail out of her way with one hand as she looked into the eyepiece.

"A symbol!" Olivia squealed as Ivy carefully drew the insignia in her notebook.

"Something wrong, ladies?" Mr. Strain called. Olivia looked up. "Sorry, Mr. Strain," she said, smiling. "It's just that there's more to my . . . cheek than I ever realized!"

Ivy took her ring out from under the lens. Olivia replaced it with her own and bent back down over the eyepiece.

"Does yours have the same mark?" Ivy whispered.

Olivia nodded excitedly. "What do you think it is?"

"A jeweler's mark, maybe?" Ivy guessed.

Olivia looked up at her quizzically.

"Maybe the jeweler put this tiny symbol into his work," Ivy went on quietly, "the way a painter signs a painting. We might be able to use this mark to find the person who made the rings or cut the stones."

Olivia's eyes flickered as she caught on. "And that person might have a record of our parents' names!"

"I'm pretty sure that it's a vamp jeweler," Ivy said, taking a turn to look through the microscope at Olivia's ring. "I can tell from the symbol.

Vamp businesses often hide tiny marks in their signs and logos and stuff to identify themselves as vampiric. They don't always use a V, but they often do."

Mr. Strain appeared in front of their desk.

"That does not look like a cheek slide," he said sternly.

"We were just fooling around," Olivia said with a panicked glance at Ivy.

"Right," Ivy agreed. "We were being . . . ha ha . . . cheeky." Olivia giggled nervously as she returned her ring to her finger.

Ivy didn't have a chance to talk to Olivia again until they were heading home.

"Maybe we'll find out that our biological mother is a master jeweler!" Ivy said a few blocks from her house, her hands jammed in her pockets to protect them from the cold. "Maybe she made our rings herself."

"That would be cool," agreed Olivia.

Just then, Ivy's cell phone rang. "Dad," she announced, glancing at the caller ID display and flipping open the phone.

"Hello, Ivy," her father's smooth voice intoned. "Will you be joining me for dinner tonight? I am preparing hemoglobin stew with parsnips."

"Hi, Dad," Ivy said. "I'm glad you called.

Olivia's coming over this afternoon to, uh . . ." Olivia mimed reading a book and taking notes.

"Do some research," Ivy finished. "She's dying to meet you."

There was a long silence on the other end of the phone. "It is fine for Olivia to come over, but I am afraid I must leave for an appointment with a client," her father said at last.

"Can't you change it?" Ivy pleaded.

"No," her father said simply. "My regrets," he finished and hung up.

Ivy sighed, her warm breath forming a frosty cloud in the air. "The good news," she told her sister, "is that the computer will be free." She kicked a rock into a pile of frozen leaves. "The bad news is that my dad won't be there." She couldn't help feeling disappointed. Why isn't my dad more eager to meet my twin sister? she thought.

"That's okay," Olivia said, swinging her book bag onto her other shoulder and putting her arm through Ivy's. "We'll cross paths one of these days."

"He's already two hundred years old," Ivy said with a roll of her eyes. "'One of these days' could be two decades from now!"

Olivia had been to Ivy's a handful of times before, but the mansion at the top of the hill still blew her away. From the outside, the place looked like something out of a Civil War epic - or an old black-and-white vampire movie.

The inside was just as glamorous. She'd seen Ivy's basement crypt bedroom with its huge closet. And she'd helped to decorate the gothic third floor ballroom for the All Hallows' Ball, so she wasn't expecting Mr.Vega's study to be a pile of old decorating magazines on top of a bangedup filing cabinet. Still, Olivia couldn't keep from being impressed when Ivy opened the door to the study on the second floor.

All four walls were lined with bookshelves.

There was a huge mahogany desk crowned by a flat-screen computer monitor, and across the room was an enormous globe in the middle of a rug that looked like a starry sky. Next to it, on top of a wide pedestal, stood a gray model with tiny paintings on the walls.

And then Olivia looked up, and realized that the dark-wood bookshelves lining the walls stretched up for another story, and there was a narrow walkway - like a balcony - to enable browsing up there.

This place is awesome! she thought.

Ivy dragged a second high-backed blacklacquer chair behind the desk and motioned for Olivia to sit beside her as she powered up her dad's computer.

The screen lit up with a black-and-white photograph of Ivy in profile, looking thoughtful, the outline of tree branches against a sunset sky behind her.

"I wish my father would change his background," Ivy said with a sigh.

"But that's such a good picture of you!" Olivia exclaimed.

"Look at my nose," her sister scoffed. "It's huge."

"Hey," Olivia countered with mock offense.

"You better be careful what you say about our nose!"

Ivy grinned. "Are you ready for the Vorld Vide Veb?" she asked.

Olivia nodded and Ivy clicked on an icon of a moon in the corner, and the screen went black, except for three big Gothic letters in the center: V V V

"Can anyone access this?" Olivia asked.

Ivy shook her head. "Your computer needs a special chip just to get this far."

Ivy carefully started clicking on the letters: the upper left tip of the first V, then the bottom of the V, then the place where the upper right tip of the first V met the upper left of the second V. "What are you doing?" Olivia asked.

"You'll see," said Ivy. Her seventh click, on the upper right-hand corner of the third V, prompted her for a user name and password.

After Ivy had typed them in, a question appeared on the screen: How do you like your coffee? "Wow!" Olivia remarked, impressed by the site's security. "They really know a lot about you."

Ivy chuckled. "It's a riddle," she explained. "It's different every time.Want to guess?"

Olivia read the question again. "With sweetener?" she tried.

"You are such a bunny," Ivy teased. Then she typed in the letters B-L-A-C-K.

The screen flashed, and a search engine called Moonlight appeared on screen. Illuminate the darkness, it said underneath the entry box.

"Is there anything vampires don't have their own secret version of?" Olivia asked in amazement.

"A cruise liner," Ivy replied as she typed in JEWELERS' MARKS. "Vamps don't really like water."

There were 272,000 results, and the first one was the Web site for the Vampire Jewelers Association (VJA), which offered one of the most comprehensive registries of jewelers' marks in the underworld.

Ivy clicked on the link, and seconds later she and Olivia were scanning the marks of thousands of vampire jewelers. Some looked like cat's whiskers, some like tiny coffins, lots incorporated a V in some way - but none looked like the symbol on their rings.

After the VJA site, they tried the listing on the Antique Jewelry Guild site. Eventually, there was only one page of symbols left to see. Ivy took a deep breath and clicked.

The page filled with marks.

Not one even vaguely resembles the insignia on our emeralds, Olivia thought disappointedly.

Ivy sighed. "If it's not a jeweler's mark, it could be anything."

Determined to remain upbeat, Olivia suggested they try searching for something else. Ivy went back to the Moonlight page.

"Type in 'human-vampire relationships,'" Olivia instructed, so Ivy did.

Results flooded the screen: Crossbreed Born with Four Heads Mixed Offspring Eats Self to Death Monstrous Hybrid Stalks Sewers Bat Baby Terrorizes Hospital!

"W-what is all this?" Olivia stammered.

"Tabloid headlines," Ivy answered wearily.

"Vamp rags are full of over-the-top stories about what happens when a human and a vamp try to have a baby."

"They have bat babies?" Olivia said in disbelief.

"Of course not," Ivy dismissed. "Here's something that doesn't sound insane," she went on, running her cursor over a link near the bottom of the screen: "Genetic Barriers to Crossbreeding:A Scientific Study." Ivy clicked and ended up on the Web site for something called the Vampiric Journal of Biomedical Sciences.

Olivia read the summary of the article aloud.

"'This V-Gen-sponsored study compares the genetic makeup of vampires and humans in order to objectively assess the possibility of successfully bearing healthy crossbreed offspring. Findings suggest that the significant differences between vampire and human DNA amount to an insurmountable obstacle of a magnitude similar to that found between canines and felines.'" Olivia looked at her sister. "Is it just me, or does this say that you and me are about as likely as puppies born to a cat and dog?"

Ivy sighed. "That's what it says," she agreed. "But we're obviously not impossible," she went on.

"I mean, we exist and we're sisters!" She scanned the screen and then gasped suddenly. "No way!"

"What?" Olivia asked.

"This article was written by Marc Daniels.

That's Brendan's father's name!"

"Are you sure?" Olivia asked, peering at the screen. She pointed to a line at the end of the research report. "Is Brendan's dad head researcher of V-Gen?"

Ivy shrugged. She quickly went back to the main search page and typed in V-Gen. The top result said, V-GEN - a leading vampire pharmaceutical company based in Franklin Grove.

Olivia and Ivy both stared at the screen for a long moment, taking in the indisputable fact that Brendan's father was the same Marc Daniels who had written the article.

"We have to talk to him," Olivia said at last.

Ivy bit her lip. "Judging from his research, he's not really on our side," she said.

"Maybe we can change his mind," Olivia proposed.

"Even if we could, Olivia," responded Ivy, "I can't talk to my boyfriend's father about how babies are made."

"Sure you can!" Olivia laughed. "He'll understand.

Come on, Ivy.We have to get answers! Ask Brendan tomorrow if he'll introduce us to his dad. Please."

"I am not going to bring this up at school," Ivy declared decisively, and Olivia's heart sank.Then Ivy added quietly, "I have a date with Brendan on Friday. I'll ask him then."

Olivia clapped her hands. "Talking to a vampire geneticist about how we're twins is going to be way more interesting than cheek cells!"

At school on Thursday, the whole twin frenzy was even more intense than it had been the day before. After fourth period, Ivy saw a sixth-grader wearing a baby tee that said, IWANNA GOTH TWIN.

I'm a fad! Ivy thought, horrified. If she could have dug a hole, climbed into her coffin, and lowered herself into the ground, she would have. She felt so ill by the end of the day that she canceled after-school plans with Olivia - they had been going to make a list of questions for Mr. Daniels - and went straight home.

That night, Ivy was in her pajamas, reading before bed, when she heard footsteps descending the basement stairs. She watched as her father came slowly into view.

"You cleaned your room," he said approvingly.

That's when Ivy knew something was wrong, because, if anything, the basement was an even bigger mess than usual. She sat up and closed her book.

"Ivy," he said when he reached the bottom of the stairs, "I need to speak with you.

"Do you recall the hotel job I mentioned several weeks ago?" he asked.

"You mean the one in Europe?" Ivy said.

Her father nodded in confirmation. A chain of vampire-funded hotels had wanted to hire him to be their interior designer. It was a really good job, but he had said he didn't want to leave Franklin Grove.

"I've accepted the job," Mr.Vega announced.

Ivy blinked. "I thought you already said no."

"I did." He cleared his throat. "But now they have made me an offer that I cannot refuse."

"What?" gasped Ivy.

"I have to." He paused. "I would not be able to live with myself if I didn't take the job. I start in about three weeks."

A chill came over Ivy. She pulled the sleeves of her pajamas down around her wrists. "So you're going to Europe?"

Her father nodded apologetically.

"But how am I supposed to stay in Franklin Grove if you go to Europe?" she asked.

He pulled a black handkerchief from his pocket and wrung it absentmindedly. "You won't," he said, a pained look in his eyes. "You'll be coming with me."

Ivy's heart seized. "You're taking me out of school?"

"There is a very good academy for girls like you in Luxembourg," her father answered in a weary voice.

"I can't!" she cried in horror, pulling a black cat pillow in front of her.

"We must," her father said.

"All my friends are here!" Ivy pleaded.

"You will make new friends."

"What about Olivia?"

Her father studied his hands. "I'm sorry," he said quietly.

Ivy could feel tears starting to slide down her cheeks. "Why are you doing this?" she quavered.

"Ivy, I am taking this job for you," he said gently. "You will understand one day, when you are a parent."

Without saying anything more, her father started to walk away. He turned to look back at her solemnly before climbing the stairs. "We'll be moving during your winter break. I know how hard this will be for you, Ivy. But try to think of it as a new adventure. For both of us," he finished. Then he was gone.

Ivy was stunned. How can I leave Franklin Grove? How can I leave Olivia and my friends?

None of this makes sense!

Ivy instinctively reached for the phone, but then realized that it was too late to call anyone.

She buried her face in her cat pillow and stayed that way, thinking, unable to fall asleep for hours.