Big "A". Red Coat. The sicko in charge of it all. Whatever you want to call her (or possibly him), the Liars' greatest threat is still a mystery on Pretty Little Liars, which means every episode is a new piece of the puzzle. Who do we think "A" could be after Season 4, Episode 6: "Under the Gun"? We've gathered our top suspects.

3. Shana

Why she might be Big "A": How was Shana not suspicious this week? Between her sudden transfer to Rosewood and her inexplicable appearance in Ravenswood, everything about her actions screamed up to no good. She clearly has a weird fixation on Emily. Is it possible that she's hurting the Liars to avenge her love, Jenna?

Why she might not be Big “A”: According to Mona, Jenna and Shana are scared of Melissa, which doesn't exactly sound like Red Coat (unless it's an act...). Plus, we doubt the writers would make such a relatively minor character so important.

2. Jenna Marshall

Why she might be Big "A": You know all that suspicious stuff Shana did this week? Yeah, we wouldn't be at all surprised if she was doing it all at Jenna's request, so it's possible she was acting as "A"'s lackey this week. Jenna has more motivation than just about anyone to hate the Liars, and she's smart enough to pull it all off. We can never really trust her.

Why she might not be Big “A”: There are a couple of moments that don't make sense with Jenna being Big "A" (for instance, if the woman in the mask/veil at Wilden's funeral is Big "A", that rules Jenna out, since we saw her at the funeral). Plus, we prefer Jenna like she is: untrustworthy, complex, but sympathetic, and possibly as much a victim in this as the Liars.

1. Alison DiLaurentis

Why she might be Big "A": Ali is at the top of our list for all the reasons we've discussed before. This week added to the evidence: While Ms. Grunwald claimed not to know anything about Alison, she seemed to recognize the name "Vivian," so we're not so sure she's as uninvolved as it would appear. Was Ali hiding out as Vivian, perhaps?

Why she might not be Big “A”: As always, we have to acknowledge that she might actually be dead.

Of course, these aren't the only people we have our eyes on. In Rosewood, anything is possible.

Who do you think "A" is? Sound off in the comments below!

Catch the next episode of Pretty Little Liars on Tuesday, July 23, 2013 at 8 p.m. ET/PT on ABC Family.