Keegan Allen and Troian Bellisario

"Mona is back, Toby is in black and Byron may be wack." That's the mantra that Pretty Little Liars executive producer Oliver Goldstick came up with while planning Season 3B.

"This is a game-changer for us because we've never had a parent who was really a suspect," Goldstick told TVGuide.com.

Mona's Back! Pretty Little Liars boss promises return of the old "A"

Although there was a death (RIP Garrett), the return of the creepy mask and a kidnapping (poor Aria on the show's Halloween special, the biggest turn of events was the seed Garrett planted that implicated Aria's dad Byron (Chad Lowe) in Alison's murder. In the shady police officer's final moments, he told Spencer (Troian Bellisario) that he witnessed Bryon and Alison (Sasha Pieterse) fighting right before she went missing. When the show returns on Jan. 8 (8/7c, ABC Family), Aria (Lucy Hale) will not be ready to face the fact that her dad might not be who she thinks he is.

But Byron's possible culpability isn't the only major revelation the girls will deal with this season. At some point, they will learn that Spencer's boyfriend Toby (Keegan Allen) is, in fact, part of the "A team." Although the summer season finale's reveal was stunning, Goldstick maintains that the signs were there all along. "We're just returning to who Toby was in Episode 102 and 103. When he first came back to Rosewood, he was dark, he was Boo Radley, and the girls were in fear of him, what he knew and what he could do. So he has an axe to grind. If you really look back at those first episodes, you'll say this is the Toby from Season 1. We're back to that person -- this is who he is."

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So what can viewers expect from our main girls Aria, Spencer, Emily (Shay Mitchell) and Hanna (Ashley Benson) as they continue to be tormented by "A"? We break it down below.

Aria
"Ezria has the biggest hurdle they've ever faced," Goldstick says about Aria and Ezra (Ian Harding). "Ezra having a child, [Aria hiding it from him], and his discovery of it will really put a large obstacle in this relationship because now he's not dealing with hiding [his relationship with Aria]; he's dealing with a mature issue. Aria also has to deal with the fact that Ezra had a life before her and it's not just another woman -- this could tear up the relationship in the end." And don't think the "A team," won't let this one go. Expect Aria to be confronted with this secret she's keeping in the first episode back.

Hanna
How will Hanna handle Mona (Janel Parrish), her ex-BFF who turned out to be "A," back in school? "Of all the PLLs, Hanna does want so badly to give Mona the benefit of the doubt," Goldstick says. "Hanna might put out a hand towards Mona and she might get bit and she might need stitches. She might be sorry she gave more than a fingernail." Ouch.

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Emily
"Emily ... stumbles upon some Alison revelations that give her more of an active role in pursuing the mystery of what happened to her that summer," Goldstick says. "She stumbles upon something that opens up a whole new world about Alison, a portal to Alison's psychology and what she was doing that summer."

Spencer
"This is a devastating season for Spencer," Goldstick says. "She comes from a family where you really can't trust what they say and no one is really honest and now she's [been betrayed] by the one person she gave all of her trust to, Toby." And although Spencer tries to warn her half-brother Jason (Drew Van Acker) about getting close to Mona, he too may turn on her (and look awfully suspicious by the end of the premiere). "The girls are kept guessing with Jason for a long time," Goldstick adds. "Something is revealed later on in the season that will clear up Jason a lot and what his motivation is, but for right now he's someone to be wary of."

Are you excited for the return of Pretty Little Liars?

Watch a clip from the premiere below: