10/19/2011 06:59 pm ET | Updated Dec 19, 2011

'Pretty Little Liars' Star Sasha Pieterse Talks Halloween Special, 'The First Secret'

"Pretty Little Liars" is full of secrets, but did you ever wonder what started all that mystery in Rosewood? While the hit ABC Family show is on hiatus until January, fans are receiving a special treat, or trick, to tide them over.

In a special Halloween prequel to air Wednesday night, it's a year before Alison goes missing and the only drama that occupies BFFs Aria, Emily, Hanna and Spencer is scoring an invite to Noel Khan’s Halloween party. Meanwhile, the new girl is giving queen bee Alison a run for her money -- and she's more than a little upset about it.

According to Sasha Pieterse, who plays the mysterious Alison, the Halloween-themed episode will not disappoint diehard fans. "It takes the creepiness up about 100 notches," reveals the actress.

The Huffington Post recently spoke with Pieterse, who dished on some Rosewood secrets, Jenna and Alison's Gaga drama, and what's in store for Aria, Emily, Hanna and Spencer this season.

The special is called "The First Secret." What's the importance of this first secret?

There's a lot of firsts in this episode because it's a prequel. It's the beginning of the girls' friendship, so there are a few first secrets that happen with the girls and Alison. It's also the first encounter with Alison's enemy. It's before the Jenna drama, before anything happened with Ian, so it's the real beginning of things. It's also the first time you see Alison alone, and the first time you see her room, and there's a really big first secret that I'm not allowed to say.

Do you think the prequel is a nice lead-in for the upcoming spring season?

It's going to tie some things together for the viewers. It's an introduction, but at the same time, it answers some questions from Alison's point of view. The girls don't know any of these things that are going on, and they're kind of oblivious to it. It will tie together with the rest of the season, but the girls won't necessarily know it yet.

It's also going to be the first time the viewers are going to get to really know Alison, right?

You see her first vulnerable stages and, like I said, you're going to see her alone for the first time. You see her when no one is looking, and that's really important. And as the rest of the season goes on, you'll start to further see what she does when no one is looking. The suspense just continues to grow.

There's also a mysterious man in a creepy mask following the girls around. What can you dish about that?

It's especially creepy because that costume seems to be the most popular costume for the Rosewood guys, so there are a lot of people in that costume. And it gets really confusing because you don't know who is who. It definitely gets scary for the girls.

It looks like Alison is channeling a bit of Lady Gaga in this episode. Is that her costume?

Yes! It was interesting because I've never been Gaga before. It's also the beginning of Lady Gaga, too! It's set during her early stages, so it's kind of like a Lady Gaga prequel, too.

It's also going to lead to a major blowout between Alison and Jenna, who also channeled her inner Gaga, right?

We've always known that Jenna was not a good person, and because of the Toby ordeal, we understand that. But we've never really known why Alison and Jenna clash so much. And with the Halloween episode, that will finally become clear, and viewers will understand why they had such heated conversations and why they could never seem to get along. And adding fuel to that fire is the fact that they both dressed up as Lady Gaga for this party. That's never a good thing.

"The First Secret" airs Wednesday, Oct. 19, at 8 p.m. ET on ABC Family.


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