And speculate we shall! There are a number of people the woman in red could be, but we have three four guesses.
Warning: This article contains spoilers for the Pretty Little Liars book series.
Alison. Yeah. We're not letting go of the "Alison [Sasha Pieterse] is alive" theory until the show proves it 100 percent wrong. Alison remains our top pick for the Big "A". She's smart, cruel, and she knows all of the Liars' secrets. It's easy to imagine her running a group of evil stalkers, and we're even willing to believe she'd be able to trick Toby (Keegan Allen) and Mona (Janel Parrish) into working with her. The only question is, how did she fake her death? Which brings us to...
Ali's twin. In the book series, Alison had a twin, named Courtney, who is the one who actually died. There have been hints that Ali has (or had) a twin on the show, too. If the writers follow the general idea from books, than the story would be that Ali killed Courtney (which would leave her alive to be running the "A" team, see above).
On the other hand, maybe the writers decided to put a twist on the books, and Ali did die, and Courtney (or whatever the twin's name is on the show, if there is a twin) is the one running the "A" team. This could work, especially if the twin has a disturbing backstory with Ali that would give her motivation for hating the Liars.
CeCe. After Episode 23, we know CeCe (Vanessa Ray) has a reason to hate Ali, and maybe she decided to take her anger out on the Liars, too. She knows a lot of their secrets, and is clearly ruthless.
Jenna. Jenna (Tammin Sursok) has plenty of reason to hate the Liars, and she's been MIA this season, which means she could easily have been running around town in a red coat and blonde wig. That said, we'd prefer if she remains a more ambiguous character.
Who do you think is the leader of the "A" team? Share your theories in the comments below!