They walked to the front door and stopped, each of them staring uncertainly at the door.

"What do we do?" asked Simon.

"We go in," announced Caleb.

"We don't have that much time. We have to get back to Elijah," said Simon. But he said the words slowly, as if he was thinking about it.

"But there could be clues in here," said Caleb, "about where we are."

Abbey's lunch jumped hurdles in her stomach. She willed it to settle down. "We could get into trouble. What if the place isn't open to the public?"

Caleb gave his customary shrug of arms and eyebrows. "We say we made a mistake and leave." He put his hand on the door handle, as if they'd already made the decision.

"But we still have the problem that someone here seems to know who we are, and we don't know who they are," Abbey said.

"Exactly," said Caleb. "That's why we need to go in."

Simon was looking at Abbey strangely. "You all right, Ab? You're really pale."

Abbey gave a weak laugh. "Just hungry, maybe." Or about to vomit, she thought.

"Here-put my toque on. Hide your hair. If you do look like Dr. Livingstone, we don't need any more comments."

Abbey pulled the toque low over her brow. She looked at the tree again. It had a maze-like feel, for mazes and trees shared the same mathematical base, and mazes, when stretched, became trees. But her mind wouldn't stop trying to trace the branches, and it was making her dizzy.

She followed her brothers through the door, which closed with a slight rush of air behind them. The light level didn't change when they entered, and Abbey realized there was no solid roof to the building, only the same epidermal layer that covered the entire city, slightly more opaque but still allowing for sufficient natural light that no other lighting was required. A narrow hallway ran directly away from the door and came to a T-junction, branching right and left several steps away from the entrance.

Caleb and Simon headed down the hallway, their runners padding softly on the carpeted floor. Abbey's drenched feet were starting to hurt in her rubber boots, and her palms were growing similarly damp. They turned right at the T-junction and followed the new white hallway, which branched again into two more white hallways. At the third empty hallway, they stopped.

"This is bizarre," said Simon. "Where are the offices?"

Abbey leaned against the wall-very slightly, so her brothers wouldn't notice-and tried not to sink to the floor. The amplitude of oscillation of her knees reminded her of a vibrating saw she'd once seen played as a musical instrument. Could she be sick from the theoretical time travel, or coming down with some terrible local illness to which she had no antibodies?

"We should go back and go left," Abbey managed to mutter.

"Why?" said Caleb.

"The building is a maze, I think. The tree on the sign is a symbol. We should go left." Why was she saying this? She had no evidence, other than a feeling, and feelings weren't reliable.

"Say what?" Caleb asked.

"In a simply connected maze you can follow the left-hand rule. Walk forward and keep your left hand on the wall at all times."

Simon looked at her strangely; she wondered if he could see the sweat on her brow. "What makes you think this is a maze?"

"It's just a guess. I think it's the security system and part of the building design. Don't ask me why. I just have a feeling..." She trailed off. "Even if I'm wrong, going left is just as good as going right. We have no idea where we're going, and this way we'll be able to find our way out." She felt vaguely relieved at having dredged up a rational basis for acting on her feeling.

"All right, works for me." Caleb returned to their starting point and went down the left hall, his hand lightly tracing the wall. Turn after turn took them one way and then the other. Although she had tried to keep track, Abbey found herself turned around with no idea which direction they were facing, or whether they were moving deeper into the heart of the building, or skirting its edges. Then, abruptly, they stopped being offered choices of path, but the narrow halls continued to twist and turn them in and then out. The maze had become a labyrinth. Labyrinths, Abbey knew, had been created to focus the mind and produce a meditative state as one approached the center. She'd always thought she would feel impatient in a labyrinth, resenting each step that took her away rather than toward her destination, even if it was the only way to get to the destination. But the farther she walked, the more the churning in her stomach calmed, and the room began to right itself again.

By the time they came to the final corner, Abbey felt almost tranquil. She knew they must be near the center. The light falling on the walls was different, and there was the hum of voices and computer equipment. When they rounded the bend, they saw rows on rows of offices, lab tables, and cubicles filled with people at work. Some bent over computer desks, others poured solutions into beakers and Petri dishes, while still others bent over microscopes. In the center of the room, in an atrium, stood the most beautiful tree Abbey had ever seen. The structure of the tree matched the one on the sign, but this one had lush, thick green leaves. Peeling red paper bark adorned the oddly twisting trunk. It ascended skyward in a lazy, almost lopsided fashion. It was the same kind of tree-Abbey realized with a slight jolt-that marked the stones in their forest.

They gawked for a few seconds before they realized they were standing in front of a reception desk, where a red-lipped woman in a low-cut tunic smiled expectantly at them.

"Welcome to the Madrone section of Livingstone Labs. Are you here for the testing?"

"Um," Caleb said. "We're here for an appointment. With, with...Dr. Livingstone."

The red-lipped woman's eyebrows scrunched together. "He or she?" she asked, turning to her laptop. A rainbow of nail polish bottles was lined up on her desk. Her nails matched her lips.

"Um. She?" Caleb offered the woman a tentative grin.

The woman c.o.c.ked her head. "She's just left for the day."

"Oh, then-he." Caleb smiled broadly.

The red-lipped woman scrutinized them.

Abbey tried to shrink into the toque.

"Dr. Livingstone is booked for the afternoon. Are you sure you have an appointment?"

Simon stepped in. "We emailed him about our findings about heat-sensitive organisms." He smiled and, to Abbey's surprise, managed to appear somewhat handsome and charming rather than scary.

Sabrina-Abbey now saw the woman's nameplate on the desk-pursed her lips into a candied pout. She leaned forward, exposing a smooth expanse of cleavage. She inhaled, causing her bosom to swell further, and then let her breath out in a slight huff through her nose. "And who exactly are you, and where are you from?"

Simon's eyes widened slightly. "Ummm. I'm Roger, and these are my a.s.sistants, Amy and John. We're from Sinclair Labs."

"Never heard of it." Sabrina leaned back in her seat.

"We're new."

"Aren't you a little young?"

Caleb interjected. "We have a product line that contributes to youthful vigor and appearance." He lowered his voice. "It's based on the proteins."

Sabrina looked them up and down once more. "I suppose you could speak to our head of heat-sensitive organism proteins. Sit in the waiting room and I'll check." She gestured toward a bench that lay within a room made of the same epidermal material as the ceiling.

They closed the solid door behind them. The waiting room looked out onto the courtyard and tree. It was silent in the room, the epidermal walls more soundproof than they looked.

"Your a.s.sistants, huh?" Caleb asked. "Why do we always have to be the a.s.sistants?"

"Because you're short," Simon said. "What was I supposed to say?"

"Your colleagues, co-workers, a.s.sociates, head researchers."

Abbey watched as Sabrina dialed the phone. The conversation grew animated, with lots of flicks of her slick ruby nails. Abbey looked away, and then risked swiveling her eyes back. Sabrina hung up the phone and made a show of busying herself at her desk, while glancing to her left toward a door in the hallway. A pocket door slid out from the wall and sealed off the entryway from which they'd come.

"We should go," Abbey said.

Caleb didn't seem to notice that the entryway had been closed off. "I think there might be something important here to help us figure this out. Look at the tree."

Abbey grabbed at his arm, trying to draw his attention to what was happening in the reception area. "I don't think this looks good."

Simon had seen, though. "Just keep it cool, Ab," he mouthed.

A burly man with a gray sweep of hair in a security uniform came through the door to Sabrina's left. Sabrina rose immediately with her hands full of white cloth and came to the door of the waiting room, followed by the security man-who, Abbey noted, carried a firearm. "Dr. Forrester will see you. Frank will escort you, as you have to pa.s.s the vaccine-testing unit, which is a high security area with the fly flu and all. You must wear these masks."

Abbey felt a shiver pa.s.s down her body to her sweaty feet. Dr. Forrester. The name had to be a coincidence. It couldn't be Mark...or could it? They each took a mask and put it on.

Frank provided a reasonable facsimile of a smile and started walking. They moved into formation behind him, each glancing at the others as they moved down the hall, away from the entryway. The entryway that was now blocked off.

"So, Frank," said Caleb, scurrying to catch up. "You been at Livingstone long?"

"Long enough," answered Frank.

"We're making a sales pitch to Dr. Forrester. Any tips you could give us? Likes, dislikes," said Caleb.

Known a.s.sociation with men named after insects, Abbey thought.

"Only thing I know is that Dr. Forrester's mother is a real character. Lives with my mom at the Seniors' Home and still smokes a pipe," said Frank.

Abbey shot Simon a panicked look. He mimed tripping the security guard and running away, but then flashed a helpless, upturned palm gesture. Even if Simon did trip Frank, they'd never find their way out of the labyrinth and then the maze before someone caught up with them.

They walked for several minutes. Frank made no further effort to make conversation. The wind had picked up and was rippling the epidermis above them. It made no noise, like a tent would, but it was disconcerting all the same. The sun had dropped in the sky and it was now noticeably darker than it was before. Abbey wondered if Elijah, their ride home, was readying to leave. She envisioned her parents arriving home to find them absent, Wallace circling around his cage looking for dinner, and Farley in a wet heap by the door.

Down the hall she saw two doors. The door on the right looked like a regular office door with a doork.n.o.b. The one on the left had a large metal bar across it and a green, glowing exit sign above it. The main hall banked to the right, into an open laboratory area, and Abbey could hear the murmur of voices.

"Now!" mouthed Simon. He reached forward with his long limbs and stuck one directly between Frank's. The older man fell into a heaving sprawl on the floor.

"Run!" yelled Simon. "Take the left door!"

Caleb and Abbey launched forward and ran down the hall with Simon behind them.

"Wait! Kids!" Frank yelled as he scrambled to his feet.

Caleb yanked open the door. Abbey felt stunned relief to see the sky bathed in dusk. She ran faster, thighs snapping as she pulled every shred of speed out of them. As she crossed the threshold, her eyes flicked to the door on the right. The periodic table caught her attention. It was an ornate Essential Elements one, Abbey's favorite, with extra details about the periodicity of each element, including its cubic radius, melting and boiling points, uses, and a drawing of the atomic structure. Above the periodic table was a nameplate with the name Dr. A. Livingstone embossed upon it.

And then Abbey saw the stones, and she was running through wet, dark forest.

Chapter 6.

To Be an Elephant

The two backpacks rested against the bathroom cabinet. Mark hadn't wanted to leave them in his room, just in case. A tube containing one neatly rolled map leaned against the blue backpack that belonged to Abbey. He brushed each tooth with the circular movements the dentist had shown him, darting glances at the backpacks to make sure they were still there. The tube of Aim toothpaste, with the end folded over on itself several times, perched on the pink and gray speckled countertop (his mother, thankfully, had gotten her own tube after the last incident). When he was young, he thought he could see elephants in the shapes on the countertop. His mother had flown him to India when he was ten to undergo elephant therapy for autism. He'd liked the elephants, but it hadn't helped him understand people. In fact, he'd decided he really would have preferred to be an elephant.

Mark wiped his sweaty palms on a towel and reviewed the order in which the objects in the backpacks had appeared. He'd returned them to exactly the same arrangement, except he couldn't quite achieve the same careless disarray that had marked Caleb's pack. Caleb's protractor was stuck to the outside of a binder with what looked like jam, and crumpled papers nudged their way out of the binder's sides. Mark's hands had twitched as he'd flipped through the papers, fighting the urge to bring the edges into alignment, to smooth the uneven ripples. Putting everything back in the pack just as it had been nearly made Mark pa.s.s out, and the odor of warm salami in the bottom had caused bile to gather in his throat. He'd been forced to sit on his bed and study the scalloped sh.o.r.eline of eastern Oahu for several minutes to clear his head.

Abbey's backpack had been a relief. The blue pack contained heavy Physics and Chemistry textbooks, blue and red notebooks with rows of methodical notes, a calculator, a package of pH testing paper, pens, a couple of empty Petri dishes, and an empty lunch bag. The slim orange-and-pink-striped journal had made his heart pound. He'd slipped it open with shaking fingers. But it contained only physics equations, diagrams, chemistry formulas, and numbers in Abbey's cramped but neat script-except in the margins, where Abbey's pen had made a few furtive strokes: hearts and trees, Abbey Livingstone, AS and SL.

The ALICE notes in Abbey's backpack had been interesting. He'd made a copy of Abbey's notes (with his Canon PC-170 copier) and filed them in the Protex fire-resistant burglary safe with the programmable combination he'd received for his twenty-first birthday. He'd tried not to pull out the photo when he opened the safe-the photo he'd found in his mother's sock drawer under the pink-and-gray-striped socks with the individual toes that she never wore. The photo of his mother, smiling, with a young blond girl and a funny-looking man with wild hair. (Mark always tried to avoid looking at the man, as it looked, from the photo, as if he may have had poor dental hygiene.) Mark managed to slam the safe door shut just before his fingers folded around the edge of the photo, and focused instead on rotating the safe driver wheel, breathing shallowly through his nose. Combination number 09-27-12. Mark said it in his mind now. It was a tidy number. Three times three was nine, three times nine was twenty-seven, two plus seven was nine, three to the third power was twenty-seven, three times four was twelve, one plus two was three. Threes and nines. If you counted in that he got it for his twenty-first birthday, and three times seven was twenty-one, that made it doubly lucky. Three was also his favorite Horton-Strahler number for the bifurcation ratio of rivers. Making it triply lucky, which was three again. 09-27-12. And now that date had come and gone-three weeks ago-and yet he was no closer to understanding what would bring him to kill Abbey, or how he could stop it.

Abbey scrunched her eyes against the suggestion of morning filtering through her blinds. The dank smell of the forest still surrounded her. A scatter of leaves lay on her pillow-leaves that had caught in her hair as she ran blindly down through the trees on Coventry Hill last night. Her heart sc.r.a.ped the bottom of her ribcage. Yesterday hadn't been a dream either. She reached for her cell phone, which she usually kept on her nightstand, but her fingers brushed wood instead of plastic. She opened her eyes a crack and saw nothing but her lamp on the table. She no longer had a cell phone. It was lost somewhere in endless dunes of sand.

It had taken them several seconds last night to realize it was their forest they were running through, hints of dusk drifting through the branches like a blanket of black tulle. Even though none of them could understand how they had gotten home, why the stones had appeared just outside the door, they didn't slow their pace until they slammed the door of their house behind them. The blue and silver car was no longer across the street and the Forrester house sat in darkness, save for lights in Mark's room and the kitchen. Their parents had not yet returned home from the evening's campaign event.

They had conducted a quick search of the house to make sure it was empty. Farley galloped from room to room behind them, his large brown body quivering with excitement. The check complete, they ate sandwiches and potato chips in silence. After eating, Abbey lay on her bed in the dark. When the van lights streamed into the driveway, she flicked on her light and sat at her desk staring at a textbook until bed. Her parents poked their heads in with inquiries about her day. Abbey indicated she had to work on her science fair project and couldn't talk.

The house now sat still, the final breaths of night not yet giving way to the stirrings of morning. Abbey slipped her hand under her pillow and pulled out a crumpled photo of smiling kids from Science Camp 2012. She had the rise and fall of the heads etched in her mind. The sun had peeked out from behind the clouds at the second the camera clicked, illuminating Abbey's red hair in a fiery halo. Next to her, with his arm draped over her shoulder, his smile brilliant, stood Sam Livingstone. Sam Livingstone, the physicist, who lived exactly 2,435.64 kilometers away.

She shoved the photo back under her pillow. The floorboards creaked outside her room. The day had started. As she rose, a small yellow leaf drifted down from her forehead to her pink pillow. She looked in the mirror on the wall above her bed. The veins of the leaf had left an imprint on her skin. They mirrored the pattern of the tree from yesterday-a perfect Horton-Strahler ratio of three.

Mark arrived on their doorstep with their backpacks and a map tube just after their parents pulled out of the drive. His hair was slicked back, a sweep of black strands covering the bald patch on his crown. His blue cardigan gaped over the fleshy expanse of his stomach. He wore a toothy grin, but his eyes widened as he spied Farley's saliva-coated tongue and the dog began the opening maneuvers of his overly exuberant greeting ritual. Abbey grabbed Farley and pulled the Chesapeake Bay Retriever into a sit.

Caleb and Simon stared at Mark. They crowded the doorway side by side to block him from entering the house. Mark continued to smile. n.o.body said anything.

"It was nice of you to return our backpacks," Abbey finally ventured from behind her brothers. She tried to see if the knife remained on his belt, but the cardigan was too long. Surely the three of them could take him down if necessary, but not if he had the knife.

Mark thrust the backpacks and map tube at Caleb and started to speak at a brisk pace. "Your sh.o.r.eline contains areas of long fairly straight coastline with no headlands and bays. That results when you have a sh.o.r.eline where the rocks are very similar or just one type. Most sh.o.r.elines consist of many rock types and they vary in their resistance to erosion, forming a more jagged sh.o.r.eline." Mark drew a breath and prepared to continue his speech.

"Whoa, slow down man," Caleb said. "Are you saying you've figured out where it is?"

Mark made puffing noises out his nose and rocked from one foot to the other, keeping his eyes focused on the stoop, except for occasional glances at the wall over Abbey's shoulder.

Mark drew his lips back again into the strained toothy arrangement that was beginning to remind Abbey of Donkey from Shrek. "It would be very helpful if you would not interrupt me. I do not deal well with interruptions. The proximity to sh.o.r.e of the two islands that appear on your map was critical to my a.s.sessment. I have accounted for slight rises in sea level and storm erosion patterns on the current substrate type of the area, presuming that ocean currents do not flip as a result of climate change."

"And if they do?" Caleb interrupted.

Mark made the nose noise again. Farley's tail thumped the floor. "Then sh.o.r.elines around the world would be so altered that we would have no way of knowing where you were."

Caleb laughed. "Where we were? That's funny. Didn't we say it was just a school a.s.signment? We didn't go anywhere. We really appreciate your help. We'll take it from here."

Abbey and Simon stood mute.

Mark's grin lost some of its enameled intensity and he staggered backward a step, breathing heavily in and out through his nose, nodding his head with each breath. Abbey wondered if it was going to be a repeat of the bed incident.