How It Really Began.

You know that boy who lives a few doors down from you who'd just the creepiest person alive? When you're on your front porch, about to kiss your boyfriend good night, you might glimpse him across the street, just standing there. He'll randomly appear you're gossiping with your best friends—except maybe it's not so random at all. He's the black cat who seems to know your route. If he rides by your house, you think, I'm going to fail my bio exam. If he looks at you funny, watch your back.

Every town has a black-cat boy. In Rosewood, his name was Toby Cavanaugh.

"I think she needs more blush." Spencer Hastings leaned back and examined one of her best friends, Emily Fields. "I can still see her freckles."

"I've got some Clinique concealer." Alison DiLaurentis sprang up and ran to her blue corduroy makeup bag.

Emily looked at herself in the mirror propped up on Alison's living room coffee table. She tilted her face one way, then another, puckered her pink lips. "My mom would kill me if she saw me with all this stuff on."

"Yeah, but we'll kill you if you take it off," warned Aria Montgomery, who was, for her own Aria reasons, prancing around the room in a pink mohair bra she'd recently knitted.

"Yeah, Em, you look awesome," Hanna Marin agreed. Hanna sat cross-legged on the floor and kept swiveling around to check that her crack wasn't sticking out of her low-rise, slightly-too-small Blue Cult jeans.

It was a Friday night in April, and Ali, Aria, Emily, Spencer, and Hanna were having one of their typical sixth-grade sleepovers: putting way too much makeup on one another, chowing on salt-and-vinegar kettle chips, and half-watching MTV Cribs on Ali's flat-screen TV. Tonight there was the added clutter of everyone's clothes spread out on the carpet, since they'd decided to swap clothes for the rest of their sixth-grade school year.

Spencer held up a lemon-yellow cashmere cardigan to her slender torso.

"Take it," Ali told her. "It'll look cute on you."

Hanna pulled an olive corduroy skirt of Ali's around her hips, turned to Ali, and struck a pose. "What do you think? Would Sean like it?"

Ali groaned and smacked Hanna was with a pillow. Ever since they'd become friends in September, all Hanna could talk about was much she looooved Sean Ackard, a boy in their class at the Rosewood Day School, where they'd all been going since kindergarten. In fifth grade, Sean had been just another short, freckled guy in their class, but over the summer, he'd grown a couple inches and lost his baby fat. Now, pretty much every girl wanted to kiss him.

It was amazing how much could change in a year.

The girls—everyone but Ali—knew that all too well. Last year, they were just…there. Spencer was the uber-anal girl who sat at the front of the class and raised her hand at every question. Aria was the slightly freaky girl who made up dance routines instead of playing soccer like everyone else. Emily was shy, state-ranked swimmer who had a lot going on under the surface—if you just got to know her. And Hanna might've been klutzy and bumbling, but she studied Vogue and Teen Vogue, and every once in a while she'd blurt out something totally random about fashion that no one else knew.

There was something special about all of them, sure, but they lived in Rosewood, Pennsylvania, a suburb twenty miles outside Philadelphia, and everything was special in Rosewood. Flowers smelled sweeter, water tasted better, houses were just plain bigger. People joked that the squirrels spent their nights cleaning up litter and weeding errant dandelions from the cobblestone sidewalks so Rosewood would look perfect for its demanding residents. In a place everything looked so flawless, it was hard to stand out.

But somehow Ali did. With her long blond hair, heart-shaped face, and huge blue eyes, she saw the most stunning girl around. After Ali united them in friendship—sometimes it felt like she'd discovered them—the girls were definitely more than just there. Suddenly, they had an all-access pass to do things they'd never dared to before. Like changing into short skirts in the Rosewood Day girls' bathroom after they got off the bus in the morning. Or passing boys ChapStick-kissed notes in class. Or walking down the Rosewood Day hallway in an intimidating line, ignoring all the losers.

Ali grabbed a tube shimmery purple lipstick and smeared it all over her lips. "Who am I?" The others groaned—Ali was imitating Imogen Smith, a girl in their class who was a little bit too in love with her Nars lipstick.

"No, wait." Spencer pursed her bow-shaped lips and handed Ali a pillow. "Put this up your shirt."

"Nice." Ali stuffed it under her pink polo, and everyone giggled some more. The rumor was that Imogen had gone all the way with Jeffrey Klein, tenth grader, and she was having his baby.

"You guys are awful." Emily blushed. She was the most demure of the group, maybe because of her super-strick upbringing—her parents thought anything fun was evil.

"What, Em?" Ali linked her arm through Emily's. "Imogen's looking awfully fat—she should hope she's pregnant."

The girls laughed again, but a little uneasily. Ali had a talent for finding a girl's weakness, and even if she was right about Imogen, the girls all sometimes wondered if Ali was ever ripping on them when they weren't around. Sometimes it was hard to know for sure.

Then settled back into sorting through one another's clothes. Aria fell in love with an ultra-preppy Fred Perry dress of Spencer's. Emily slid a denim miniskirt up her skinny legs and asked everyone if it was too short. Ali declared a pair of Hanna's Joe's jeans too bell-bottomy and slid them off, revealing her candy-pink velour boy shirts. As she walked past the window to the stereo, she froze.

"Oh my God!" she screamed, running behind the blackberry-colored velvet couch.

The girls wheeled around. At the window was Toby Cavanaugh. He was just…standing there. Staring at them.

"Ew, ew, ew!" Aria covered up her chest—she had taken off Spencer's dress and was again in her knitted bra. Spencer, who was clothes, ran up to the window. "Get away from us, perv!" she cried. Toby smirked before he turned and ran away.

When most people saw Toby, they crossed to the other side of the street. He was a year older than the girls, pale, tall, and skinny, and was always wandering around the neighborhood alone, seemingly spying on everyone. They'd heard rumors about him: that's he'd been caught French-kissing his dog. That he was such a good swimmer because he had fish gills instead of lungs. That he slept in a coffin in his backyard tree house every night.

There was only one person Toby spoke to: his step-sister, Jenna, who was in their grade. Jenna was a hopeless dork as well, although far less creepy—at least she spoke in complete sentences. And she was pretty in an irksome way, with her thick, dark hair, huge, earnest green eyes, and pursed red lips.

"I feel, like, violated." Aria wriggled her naturally thin body as if it were covered in E. coli. They'd just learned about it in science class. "How dare he scare us?"

Ali's face blazed red with fury. "We have to get him back."

"How?" Hanna widened her light brown eyes.

Ali thought for a minute. "We should him a taste of his own medicine."

The thing to do, she explained, was to scare Toby. When Toby wasn't skulking around the neighborhood, spying on people, he was guaranteed to be in his tree house. He spent every other waking second there, playing with his Game Boy or, who knows, building a giant robot to nuke Rosewood Day. But since the tree house was, obviously, up in a tree—and because Toby pulled up the rope ladder so no one could follow him—they couldn't just peek in and say boo. "So we need fireworks. Luckily, we know just where they are." Ali grinned.

Toby was obsessed with fireworks; he kept a stash of bottle rockets at the base of the tree and often set them off through his tree house's skylight. "We sneak over there, steal one, and light it at his window," Ali explained. "It'll totally freak him out."

The girls looked at the Cavanaugh house across the street. Although most of the lights were already out, it wasn't that late—only ten-thirty. "I don't know," Spencer said.

"Yeah," Aria agreed. "What if something goes wrong?"

Ali sighed dramatically. "C'mon, guys."

Everyone was quiet. Then Hanna cleared her throat. "Sounds good to me."

"All right." Spencer caved. Emily and Aria shrugged in agreement.

Ali clapped her hands and gestured to the couch by the window. "I'll go do it. You can watch from here."

The girls scrambled over to the great room's big bay window and watched Ali slip across the street. Toby's house has kitty-corner to the DiLaurentises' and built in the same impressive Victorian style, but neither house was as big as Spencer's family's farm, which bordered Ali's backyard. The Hastings compound had its own windmill, eight bedrooms, a five-car detached garage, a rock-lined pool, and a separate barn apartment.

Ali ran around to the Cavanaughs' side yard and right up to Toby's tree house. It was partially obscured by tall elms and pines, but the streetlight illuminated it just enough for them to see its vague outline. A minute later, they were pretty sure they saw Ali holding a cone-shaped firework in her hands, stepping about twenty feet back, far enough so that she had a clear view into the tree house's flickering blue window.

"Do you think she's really going to do it?" Emily whispered. A car slid past, brightening Toby's house.

"Nah," Spencer said, nervously twirling the diamond studs her parents had bought her for getting straight A's on her last report card. "She's bluffing."

Aria put the tip of one of her black braids in her mouth. "Totally."

"How do we know Toby's even in there?" Hanna asked.

They fell into an edgy silence. They'd been in on their fair share of Ali's pranks, but those had been innocent—sneaking into the saltwater hot tub at Fermata spa when they didn't have appointments, putting droplets of black dye into Spencer's sister's shampoo, sending fake secret admirer letters from Principal Appleton to dorky Mona Vanderwaal in their grade. But something about this made them all just a little…uneasy.

Boom!

Emily and Aria jumped back. Spencer and Hanna pressed their faces against the window. It was still dark across the street. A brighter light flickered from the tree house window, but that was all.

Hanna squinted. "Maybe that wasn't the firework."

"What else could it have been?" Spencer said sarcastically. "A gun?"

Then the Cavanaughs' German shepherd started to bark. The side patio light snapped on. these were loud voices, and Mr. Cavanaugh burst out the side door. Suddenly, little fingers of fire leapt up from the tree house window. The fire started to spread. It looked like the video Emily's parents made her watch every year at Christmas. Then came the sirens.

Aria looked at the others. "What's going on?"

"Do you think…?" Spencer whispered.

"What if Ali—" Hanna started.

"Guys." A voice came from behind them. Ali stood in the great room doorway. Her arms were at her sides and her face was pale—paler than they'd ever seen it before.

"What happened?" everyone said at once.

Ali looked worried. "I don't know. But it wasn't my fault."

The siren got closer and closer…until an ambulance wailed into the Cavanaugh driveway. Paramedics poured out and rushed to the tree house. The rope had been lowered down.

"What happened, Ali?" Spencer turned, heading out the door. "You've got to tell us what happened?"

Ali started after her. "Spence, no."

Hanna and Aria looked at each other; they were too afraid to follow. Someone might see them.

Spencer crouched behind a bush and looked across the street. That was when she saw the ugly, jagged hole in Toby's tree house window. She felt someone creeping up behind her. "It's me," Ali said.

"What—" Spencer started, but before she could finish, a paramedic began climbing back down the tree house, and he had someone in his arms. Was Toby hurt? Was he…dead?

All the girls, inside and out, craned to see. Their hearts began to beat faster. Then, for just a second, they stopped.

It wasn't Toby. It was Jenna.

Several minutes later, Ali and Spencer came back inside. Ali told them all what happened with an almost-eerie calmness: the firework had gone through the window and hit Jenna. No one had seen her light it, so they were safe, as long as they all kept quiet. It was, after all, Toby's firework. If the cops would blame anyone, it would be him.

All night, they cried and hugged and went in and out of sleep. Spencer was so shell-shocked, she spent hours curled in a ball, wordlessly flicking from E! to the Cartoon Network to Animal Planet. When they awoke the next day, the news was all over the neighborhood: someone had confessed.

Toby.

The girls thought it was a joke, but the local paper confirmed that Toby had admitted to playing with a lit firework in his tree house, accidentally sending one at his sister's face…and the firework had blinded her. Ali read it out loud as they all gathered around her kitchen table, holding hands. They knew they should be relieved, except…they knew the truth.

The few days that Jenna was in the hospital, she was hysterical—and confused. Everyone asked her what had happened, but she didn't seem to remember. She said she couldn't recall anything that happened right before the accident, either. Doctors said it was probably post-traumatic stress.

Rosewood Day held a don't-play-with-fireworks assembly in Jenna's honor, followed by a benefit dance and a bake sale. The girls, especially Spencer, participated overzealously although of course they pretended not to know anything about what had happened. If anyone asked, they said that Jenna was a sweet girl and one of their closest pals. A lot of girls who'd never spoken to Jenna were saying the exact same thing. As for Jenna, she never came back to Rosewood Day. She went to a special school for the blind in Philadelphia, and no one saw her after that night.

Bad things in Rosewood were all eventually gently nudged out of sight, and Toby was no exception. His parents homeschooled him for the remainder of the year. The summer passed, and the next school year Toby went to a reform school in Maine. He left unceremoniously one clear day in mid-August. His father drove him to the SEPTA station, where he took the train to the airport alone. The girls watched as his family tore down the tree house that afternoon. It was like they wanted to erase as much of Toby's existence as possible.

Two days after Toby left, Ali's parents took the girls on a camping trip to the Pocono Mountains. The five of them went white-water rafting and rock-climbing, and tanned on the banks of the lake. At night, when their conversation turned to Toby and Jenna—as it often did that summer—Ali reminded them that they could never, ever tell anyone. They'd all keep the secret forever…and it would bond their friendship into eternity. That night, when they zipped themselves into their five-girl tent, J. Crew cashmere hoodies up around their heads, Ali gave each of them a brightly colored string bracelet to symbolize the bond. She tied the bracelets on each of their wrists and told them to repeat after her: "I promise not to tell, until the day I die."

They went around in a circle, Spencer to Hanna to Emily to Aria, saying exactly that. Ali tired on her bracelet last. "Until the day I die," she whispered after making the knot, her hands clasped over her heart. Each of the girls squeezed hands. Despite the dreadfulness of the situation, they felt lucky to have each other.

The girls wore their bracelets through showers, spring break trips to D.C. and Colonial Williamsburg—or, in Spencer's case, to Bermuda—through grubby hockey practices and messy bouts with the flu. Ali managed to keep her bracelet the cleanest of everyone's, as if getting it dirty would cloud its purpose. Sometimes, they would touch their fingers to the bracelet and whisper, "Until the day I die," to remind themselves of how close they all were. It became their code; they all knew what it meant. In fact, Ali said it less than a year later, the very last day of seventh grade, as the girls were starting their summer-kickoff sleepover. No one knew that in just a few short hours, Ali would disappear.

Or that it would be the day she died.