Janel Parrish

If you thought Pretty Little Liars was insane last season, just wait for Season 3.

"It's going to be darker and more intense," Janel Parrish, who plays the villainous A, tells TVGuide.com.

When viewers last saw Aria (Lucy Hale), Spencer (Troian Bellisario), Emily (Shay Mitchell) and Hanna (Ashley Benson), the quartet had finally uncovered the series-long mystery of A's identity. After dead-end clues, cryptic texts, tons of torment and even death, A was revealed to be Hanna's former best friend Mona (Parrish). When the ABC Family show returns on Tuesday (8/7c), the summer will have passed, Mona will still be locked up and the "A" messages will have gone radio silent — until, of course, an incident in the opening minutes of the premiere.

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"Something very important goes missing," Parrish says. (If you've seen this preview, it's pretty clear the something is a body.) The incident soon triggers a new adversary to communicate with the girl and from that moment on, Parish says viewers will be tasked with trying to solve the show's next major question. "You're going to find out whether Mona is working with this person, if they're working for her or if she's working for them," she says. "It's going to be the new big mystery for the show."

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For the actress, playing Mona-as-A is completely different. "That's the most challenging part about it," she says. "I'm basically creating a whole new character and she's more unpredictable and smarter than everyone thought she was. There are all these different colors to her character that have never been seen before." Currently, Mona resides in the psych ward, but viewers will still learn more about her motivations. "There are no limits to Mona's craziness, but people are going to change their mind about her," she says. "I think it will be shocking [to learn] the people you can't trust [are those] you think you can."

Watch a sneak peek from the Season 3 premiere: