Pretty Little Liars

Pretty Little Liars' second season finale will finally answer one of the show's biggest questions: Who is A?

The ABC Family drama began a year after the murder of Queen B Alison (Sasha Pieterse), when her surviving quartet of friends began receiving mysterious texts signed with the letter "A." When the sender of those messages is revealed in the Season 2 finale (Monday, 8/7c), executive producer Marlene King says viewers won't feel blind-sided.

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"When people find out who A is and what A's motivation is, they will feel that, looking back, it all makes sense," King tells TVGuide.com.

Of all the characters to have come and gone in Rosewood, who is the most likely candidate to be A? We asked King to weigh in on our best guesses.

Jenna (Tammin Sursok)
For Her: Jenna has motive: She went blind thanks to an accident caused by Alison (Sasha Pieterse), Aria (Lucy Hale), Emily (Shay Mitchell), Hanna (Ashley Benson) and Spencer (Troian Bellisario). She and Garrett (Yani Gellman) also pretty much confessed to Alison's murder in the midseason finale. Plus: She's lying about the success of her eye surgery.
Against Her: In Episode 23, someone lured Jenna to a house that blew up. After the clear attempt on Jenna's life, she apologized to the girls, saying, "I've never been the person you really need to fear."
King Says: "We'll definitely see more of Jenna in the finale," King says. And will the girls learn that Jenna is lying about her ability to see? "Eventually it will be addressed, but I won't say if it's addressed in the finale."

Mona (Janel Parrish)
For Her: She was tormented by Alison for years and her friendship with Hanna has given her access to the girls. SPOILER ALERT! She was also the original A in the book series that inspired the show.
Against Her: She's been an ally to the foursome in the second half of the season and has also started to receive texts from A.
King Says: Mona's role has increased on the show because "some people click," King says. "We felt this way about [Mona]. It was such a fun character we fell more and more in love with her as the show went on."

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Melissa (Torrey DeVito)
For Her: Where do we begin? When the girls made sure Melissa would catch Caleb "cheating" on Hanna, they received a text from A about the affair moments later. Earlier this season, Melissa's then-fiancé Ian confessed to Alison's murder in his suicide note, but could he have done it to protect her? Then, there's the finale preview clip below and the fact that Melissa was also in the video from the night of Alison's disappearance. Oh, and she's dating Garrett!
Against Her: It just seems too obvious. What if she and Garrett are being framed? 
King Says: "All those people we see... on that video tape on the night Ali was murdered, we refer to them as the NAT club. And you can't trust anybody in the NAT club!" King says. "There's still more about the NAT club and more about that night we haven't discovered yet."

Alison's twin
For Her: The Halloween prequel episode hinted that Alison was actually a twin (like she was in the books). If the story Alison told about two young twins was really about herself, then her sister was sent to a mental hospital when she was little and could be very jealous of her sister. The girls also learned from Duncan that Alison was acting "different" the day she disappeared. Maybe it was really her sister. That could also explain Spencer and Emily's vivid dreams about Alison. What if they weren't dreams at all?
Against Her: We don't know much about the twin and her current whereabouts.
King says: "People like to make that assumption ... but I don't think we've ever confirmed that Alison was a twin. We laid the groundwork for that being a possibility," she says.

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Toby (Keegan Allen)
For Him: He's Jenna's step-brother, so he shares many of her reasons for hating the girls. He's recently become very distant and angry with his ex-girlfriend Spencer, and he has a tattoo that says, "901 Free At Last." (Alison died on Sept. 1, aka 9/01.) Plus, he's got the physical strength we've seen A display in fights at the greenhouse and the bell tower.
Against Him: He seems too innocent to hurt people!
King Says: "We do find out in the finale that Toby has a secret of his own."

Who do you think A is?

Watch a clip from the premiere:

The Pretty Little Liars finale airs Monday at 8/7c on ABC Family.