One: And We Thought We Were Friends.

Spencer Hastings stood on the apple-green lawn of the Rosewood Abbey with her three ex-best friends, Hanna Marin, Aria Montgomery, and Emily Fields. The girls had stopped speaking more than three years ago, not long after Alison DiLaurentis mysteriously went missing, but they'd been brought back together today for Alison's memorial service. Two days ago, construction workers had found Ali's body under a concrete slab behind what used to be her house.

Spencer looked again at the text message she'd just received on her Sidekick.

I'm still here, bitches. And I know everything. —A

"Oh my God," Hanna whispered. Her BlackBerry's screen read the same thing. So did Aria's Treo and Emily's Nokia. Over the past week, each of them had gotten e-mails, texts, and IMs from someone who went by the initial A. The notes had mostly been about stuff from seventh grade, the year Ali went missing, but they'd also mentioned new secrets…stuff that was happening now.

Spencer thought A might have been Alison—that somehow she was back—except that was out of the question now, right? Ali's body had decayed under the concrete. She'd been…dead…for a long, long time.

"Do you think this means…The Jenna Thing?" Aria whispered, running her hand over her angular jaw.

Spencer slid her phone back in her tweed Kate Spade bag. "We shouldn't talk about this here. Someone might hear us." She glanced nervously at the abbey's steps, where Toby and Jenna Cavanaugh had stood just a moment before. Spencer hadn't seen Toby since before Ali even went missing, and the last time she saw Jenna was the night of her accident, limp in the arms of the paramedic who'd carried her down.

"The swings?" Aria whispered, meaning the Rosewood Day Elementary playground. It was their old special meeting place.

"Perfect," Spencer said, pushing through a crowd of mourners. "Meet you there."

It was the late afternoon on a crystal-clear fall day. The air smelled like apples and wood smoke. A hot-air balloon floated overhead. It was a fitting day for a memorial service for one of the most beautiful girls in Rosewood.

I know everything.

Spencer shivered. It had to be a bluff. Whoever this A was, A couldn't know everything. Not about The Jenna Thing…and certainly not about the secret only Spencer and Ali shared. The night of Jenna's accident, Spencer had witnessed something that her friends hadn't, but Ali had made her keep it a secret, even from Emily, Aria, and Hanna. Spencer had wanted to tell them, but when she couldn't, she pushed it aside and pretended that it hadn't happened.

But…it had.

That fresh, springy April night in sixth grade, just after Ali shot the firework into the tree house window, Spencer ran outside. The air smelled like burning hair. She saw the paramedics bringing Jenna down the tree house's shaky rope ladder.

Ali was next to her. "Did you do that on purpose?" Spencer demanded, terrified.

"No!" Ali clutched Spencer's arm. "It was—"

For years, Spencer had tried to block out what had come next: Toby Cavanaugh coming straight for them. His hair was matted to his head, and his goth-pale face was flushed. He walked right up to Ali.

"I saw you." Toby was so angry he was shaking. He glanced toward his driveway, where a police car had pulled in. "I'm going to tell."

Spencer gasped. The ambulance doors slammed shut it's sirens screamed away from the house. Ali was calm. "Yeah, but I saw you, Toby," she said. "And if you tell, I'll tell, too. Your parents."

Toby took a step back. "No."

"Yes," Ali countered. Although she was only five-three, suddenly she seemed much taller. "You lit the firework. You hurt your sister."

Spencer grabbed her arm. What was she doing? But Ali shook her off.

"Stepsister," Toby mumbled, almost inaudibly. He glanced at his tree house and then toward the end of the street. Another police car slowly rolled up to the Cavanaugh house. "I'll get you," he growled to Ali. "You just wait."

Then he disappeared.

Spencer grabbed Ali's arm. "What are we going to do?"

"Nothing," Ali said, almost lightly. "We're fine."

"Alison…" Spencer blinked in disbelief. "Didn't you hear him? He said he saw what you did. He's going to tell the police right now."

"I don't think so." Ali smiled. "Not with what I've got on him." And then she leaned over and whispered what she'd seen Toby do. It was something so disgusting Ali had forgotten she was holding the lit firework until it shot out of her hands and through the tree house window.

Ali made Spencer promise not to tell the others about any of it, and warned that if Spencer did tell them, she'd figure out a way for Spencer—and only Spencer—to take the heat. Terrified at what Ali might do, Spencer kept her mouth shut. She worried that Jenna might say something—surely Jenna remembered that Toby hadn't done it—but Jenna had been confused and delirious…she'd said that night was a blank.

Then, a year later, Ali went missing.

The police questioned everyone, including Spencer, asking if there was anyone who wanted to hurt Ali. Toby, Spencer thought immediately. She couldn't forget the moment when he'd said: I'll get you. Except naming Toby meant telling the cops the truth about Jenna's accident—that she was partially responsible. That she'd known the truth all this time and hadn't told anyone. It also meant telling her friends the secret she'd been keeping for more than a year. So Spencer said nothing.

Spencer list another Parliament and turned out of the Rosewood Abbey parking lot. See? A couldn't possibly know everything, like the text had said. Unless, that was, A was Toby Cavanaugh… But that didn't make sense. A's note to Spencer were about a secret that only Ali knew: back in seventh grade, Spencer had kissed Ian, her sister Melissa's boyfriend. Spencer had admitted what she'd done to Ali—but no one else. And A also knew about Wren, her sister's now-ex, whom Spencer had done more than just kiss last week.

But the Cavanaughs did live on Spencer's street. With binoculars, Toby might be able to see in her window. And Toby was in Rosewood, even though it was September. Shouldn't he be at boarding school?

Spencer pulled into the brick-paved driveway of the Rosewood Day School. Her friends were already there, huddling by the elementary school jungle gym. It was a beautiful wooden castle, complete with turrets, flags, and a dragon-shaped slide. The parking lot was deserted, the brick walkways were empty, and the practice fields were silent; the whole school had the day off in Ali's memory.

"So we all got texts from this A person?" Hanna asked as Spencer approached. Everyone had her cell phone out and was staring at the I know everything note.

"I got two others," Emily said tentatively. "I thought they were from Ali."

"I did too!" Hanna gasped, slapping her hand on the climbing dome. Aria and Spencer nodded as well. They all looked at one another with wide, nervous eyes.

"What did yours say?" Spencer looked at Emily.

Emily pushed a lock of blondish-red hair out of her eye. "It's…personal."

Spencer was so surprised, she laughed aloud. "You don't have any secrets, Em!" Emily was the purest, sweetest girl on the planet.

Emily looked offended. "Yeah, well, I do."

"Oh." Spencer plopped down on one of the slide's steps. She breathed in, expecting to smell mulch and sawdust. Instead she caught a whiff of burning hair—just like the night of Jenna's accident. "How about you, Hanna?"

Hanna wrinkled her pert little nose. "If Emily's not talking about hers, I don't want to talk about mine. It was something only Ali knew."

"Same with mine," Aria said quickly. She lowered her eyes. "Sorry."

Spencer felt her stomach clench up. "So everyone has secrets only Ali knew?"

Everyone nodded. Spencer snorted nastily. "I thought we were best friends."

Aria turned to Spencer and frowned. "So what did yours say, then?"

Spencer didn't feel like her Ian secret was all that juicy. It was nothing compared to what else she knew about The Jenna Thing. But now she felt too proud to tell. "It's a secret Ali knew, same as yours." She pushed her long dirty-blond hair behind her ears. "But A also e-mailed me about something that's happening now. It felt like someone was spying on me."

Aria's ice-blue eyes widen. "Same here."

"So there's someone watching all of us," Emily said. A ladybug landed delicately on her shoulder, and she shook it off as though it were something much scarier.

Spencer stood up. "Do you think it could be…Toby?"

Everyone looked surprised. "Why?" Aria asked.

"He's part of The Jenna Thing," Spencer said carefully. "What if he knows?"

Aria pointed to the text on her Treo. "You really think this is about…The Jenna Thing?"

Spencer licked her lips. Tell them. "We still don't know why Toby took the blame," she suggested, testing to see what the others would say.

Hanna thought for a moment. "The only way Toby could know what we did is if one of us told." She looked at the others distrustfully. "I didn't tell."

"You mean if someone else saw Ali that night and told him?" Aria asked. "Or if he saw Ali?"

"No…I mean…I don't know," Spencer said. "I'm just throwing it out there."

Tell them, Spencer thought again, but she couldn't. Everyone seemed wary of one another, sort of like it had been right after Ali went missing, when their friendship disintegrated. If Spencer told them the truth about Toby, they'd hate her for not having told the police when Ali disappeared. Maybe they'd even blame her for Ali's death. Maybe they should. What if Toby really had…done it? "It was just a thought," she heard herself saying. "I'm probably wrong."

"Ali said no one knew except for us." Emily's eyes looked wet. "She swore to us. Remember?"

"Besides," Hanna added, "how could Toby know that much about us? I could see it being one of Ali's old hockey friends, or her brother, or someone else actually spoke to. But she hated Toby's guts. We all did."

Spencer shrugged. "You're probably right." As soon as she said it, she relaxed. She was obsession over nothing.

Everything was quiet. Maybe too quiet. A tree branch snapped close by, and Spencer whirled around sharply. The swings swayed back and forth, as if someone had just jumped off. A brown bird perched atop of Rosewood Day Elementary roof glared at them, as if it knew things, too.

"I think someone's just trying to mess with us," Aria whispered.

"Yeah," Emily agreed, but she sounded as unconvinced.

"So, what if we get another note?" Hanna tugged her short black dress over her slender thighs. "We should at least figure out who it is."

"How about, if we get another note, we call each other," Spencer suggested. "We could try to put the pieces together. But I don't think we should do something, like, crazy. We should try not to worry."

"I'm not worried," Hanna said quickly.

"Me neither," Aria and Emily said at the same time. But when a horn honked on the main road, everyone jumped.

"Hanna! Mona Vanderwaal, Hanna's best friend, poked her pale blond head out of the window of a yellow Hummer H3. She wore large, pink-tinted aviator sunglasses.

Hanna looked at the others unapologetically. "I've gotta go," she murmured, and ran up the hill.

Over the last few years, Hanna had reinvented herself into one of the most popular girls at Rosewood Day. She'd lost weight, dyed her hair a sexy dark auburn, got a whole new designer wardrobe, and now she and Mona Vanderwaal—also a transformed dork—pranced around school, too good for everyone else. Spencer wondered what Hanna's big secret could be.

"I should go too." Aria pushed her slouchy purple purse higher on her shoulder. "So…I'll call you guys." She headed for her Subaru."

Spencer lingered by the swings. So did Emily, whose normally cheerful face looked drawn and tired. Spencer put a hand on Emily's freckled arm. "You all right?"

Emily shook her head. "Ali. She's—"

"I know."

They awkwardly hugged, then Emily broke away from the woods, saying she was going to take the shortcut home. For years, Spencer, Emily, Aria, and Hanna hadn't spoken, even if they sat behind one another in history class or were alone together in the girls' bathroom. Yet Spencer knew things about all of them—intricate parts of their personalities only a close friend could know. Like, of course Emily was taking Ali's death the hardest. They used to call Emily "Killer" because she defended Ali like a possessive Rottweiler.

Back in her car, Spencer sank into the leather seat and turned on the radio. She spun the dial and found 610 AM, Philly's sports radio station. Something about over-testosteroned guys barking about Phillies and Sixers stats calmed her. She'd hoped talking to her old friends might clear some things up, but now things just felt even…ickier. Even with Spencer's massive SAT vocabulary, she couldn't think of a better word to describe it than that.

When her cell phone buzzed in her pocket, she pulled it out, thinking it was probably Emily or Aria. Maybe even Hanna. Spencer frowned and opened her inbox.

Spence, I don't blame you for not telling them our little secret about Toby. The truth can be dangerous—and you don't want them getting hurt, do you? —A