Sasha Pieterse

The truth shall set you free. But trust us, it is not always pretty.

"The title of the season finale is 'A Is for Answers,' and it really is the answer episode," promises Pretty Little Liars executive producer Marlene King, who also directed the hour. "We've been planning this episode since midway through last season and have steadily built to it since the start of this season."

For PLL fans, the ­moment of truth has been brewing since the pilot, when Rosewood High's queen bee, Alison DiLaurentis (Sasha Pieterse), was presumed dead after going missing during a boozy hangout with pals Aria Montgomery (Lucy Hale), Spencer Hastings (Troian Bellisario), Hanna Marin (Ashley Benson) and Emily Fields (Shay Mitchell). Four seasons and countless red herrings later, viewers recently learned that Ali — an overly sexual instigator fond of older men and abusing her friends for sport — didn't actually meet her maker.

She has spent the past few years hiding from A, the show's central, unseen stalker, who's been trying to off Ali's four former besties. So who — or what — sent Ali running scared?

"That is the biggest question," says Pieterse, the 18-year-old beauty behind ABC Family's answer to Laura Palmer. "What actually happened to Ali the night she disappeared?" A lot, according to King, and all will unfold through flashbacks in the finale once Ali reunites with the girls to unmask their common foe. "She thinks that if she shares her story and tells them everything, together they will be able to figure out who A is," explains King, adding, "Ali was afraid A was going to kill her that night, so her plan was to poke the bear and go after every single person it could possibly be in hopes of eliminating them one by one." Considering the list of suspects includes half the town, "Ali was very busy," says King with a laugh.

In addition to Ali's activities, the season finale will revisit Spencer's still-unexplained time away from her friends that fateful night, as well as what really went on while the girls were all asleep in the Hastingses' barn. "I can't share much, but I will say that a lot more happened in that barn than any of us had imagined," teases Hale. We will also find out who pushed Ali's (much older) secret beau, Ian (Ryan Merriman), off the bell tower in the Season 1 finale and see the return of an iconic garden tool. "Let's just say we find out what part the shovel played," Bellisario says. But the real jaw-dropper apparently comes when Ali tells the girls a secret that King calls "devastating."

"Even as I am picturing it, the hair is raising on the back of my neck," King confesses of the haunting shocker. "It comes out of nowhere and yet makes so much sense." It also makes for PLL's darkest twist yet. "Ali tells the girls that she's never been able to find the words to say it out loud — that's why she hasn't told them about it. When we filmed this part of the episode, it was just tears and tears for days," King says. "Pardon the pun, but the girls all just brought their A game."

"It made me sad to read it, and it was sad to film, but I think it's important for the fans to see," says Pieterse, who believes this "important part of the story" could potentially alter the way Ali's loved ones — and viewers — perceive the troublemaking teen. "You see that Alison DiLaurentis is a real person. This confession makes it such a reality for the girls. They're like, 'Oh, my God, this kind of thing actually happened to one of our friends.'"

While emotions run high on screen, off camera the flashbacks have left the actresses with nothing but smiles about their early days in Rosewood, Pennsylvania. "We shot the pilot in Vancouver four years ago, when we didn't know each other at all," recalls Bellisario, praising both her castmates and the show's crew for crafting a picture-perfect replica of the original barn on the WB backlot. "We've grown so much as a family that it felt like coming home. I didn't have to wonder what my relationship with Hanna or Emily was like, because it was in my bones." It was also in Hale's hair: Yes, the streaks are back. "I've always loved that pink hair," she happily admits. "I wish Aria could have it all the time."

Sounds as though Aria and the rest of the gang will have more hair-raising concerns to deal with come Season 5 (which kicks off in June), especially if Rosewood's resident bad girl is finally safe to come home. "As you'll see in the finale, Ali appears to have become a changed person," King says. "But can people really change?"

Pretty Little Liars airs Tuesday at 8/7c on ABC Family.

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