In Pretty Little Liars Season 4, Episode 9: “Into the Deep,” someone tried to kill Jenna, presumably to keep her from spilling information she has about Alison. What Alison-based secret does Jenna have that is worth killing for?! Here are our five top theories:

Alison has a twin

Yep. We’re still on this - because it makes total sense! (In the world of PLL.) It also has book precedent. In the book series, Jenna found out about Ali’s twin, Courtney, and the two bonded over sibling issues. Could something similar have happened in the television show? Did Alison actually open up to Jenna about her twin sister - or perhaps it was Courtney who revealed the truth to Jenna?

Alison killed Marion Cavanaugh

This whole Toby’s mom thing has to tie in with the central mystery, right? We know that Wilden changed the official police report to reflect that Marion Cavanaugh jumped from the window, rather than the roof. Was he covering for Alison, who had some part in her death? Could Jenna have found out about it? Perhaps, from Wilden, who Jenna was seen helping after Ashley Marin hit him with her car in Season 3.

Alison faked her own death

We’re still not convinced that Ali didn’t fake her own death. She specifically told Spencer she was keeping a journal that Spencer could read after she’d died. If Ali’s “murder” was a plan, could she have let Jenna in on it? It seems like the kind of thing that might take more than one person to pull off.

Cece Drake killed Alison

Cece is a hot name to drop this season. Most recently, she was mentioned when Shana revealed to Spencer that Cece is the person Jenna is afraid of. Shana didn’t give a reason for this Cece-phobia, but we’re guessing it has something to do with what Jenna knows about Alison. Could Jenna be afraid of Cece because Cece killed Alison, and they both know that Jenna knows it?

Alison is not a natural blonde

Alison is known for her head of gorgeous, flaxen hair - but what if it’s all a ruse?! What if Alison’s locks are actually more of a dishwater blonde or - dare we say it - light brown? If Jenna somehow discovered Ali’s secret, who knows what lengths Ali would have gone to and - after a fake death to secretly undergo hair oxidation treatment - would still go to to keep Jenna quiet...

What do you think Jenna knows about Alison? Share your theories in the comments below!

Catch the next episode of Pretty Little Liars on Tuesday, August 13, 2013 at 8 p.m. ET/PT on ABC Family.

Credit: Celebified Photo: Pretty Little Liars' Lucy Hale Talks Season 4, Ravenswood, And Making Out With Both Ezra And Jake On-set!