Credit: ABC Family

Pretty Little LiarsSpencer Hastings (Troian Bellisario) has a big secret related to the night Alison disappeared, and we’re dying to know what it is. In the meantime, we’ve outlined our three best theories on what Spence has been hiding from her besties since before the pilot. Yeah, people, this could be show-shattering...

Spencer Buried Ali in That Grave

We know that Spencer and Alison were in a fight the night Alison was buried in a grave Mrs. Grunwald pulled her out of. Alison told Spencer that, if she didn’t fess up to Melissa about the kiss she’d shared with Ian, then Alison was going to tell Spencer’s big sis herself. The next morning. Did Spencer freak out, and try to silence Alison for good? It seems crazy and drastic and would make us very sad, but it would certainly explain why Alison has been so hesitant to trust the Liars, why Spencer followed Emily to that meeting with Ali, and why Alison fled when Spence showed herself.

Spencer Helped Alison Fake Her Death

On the flip side, Spencer could have helped Alison fake her death. We’ve always wondered if Spencer had something to do with Ali’s disappearance, given the fact that she was missing when the other Liars woke up at the sleepover. And, if only one is smart enough to pull off a ruse of this scale, it’s totally Spencer. It would also explain Spencer’s obsession with finding out who “A” is. If she has known this entire time that her friend’s safe return hinged on her discovery of whom tried to kill her, then it would certainly put an added pressure on the search.

Spencer Saw Ian That Night/Saw Alison Do Something Terrible

If Spencer was planning on telling Melissa about her and Ian the next morning, then we wouldn’t be surprised if she first wanted to give Ian a heads up that the truth was about to come out. Did Spencer sneak out that night to see Ian? We’re not sure what effect this would have on the Liars, given that Ian is long-dead, but it might be relevant if Spencer saw something else while she was out. When Spencer wandered back into the sleepover, she looked seriously out-of-it. Did she see Alison do something terrible? Perhaps, kill Sara Harvey as part of her plan to disappear? We’ve been wondering how Sara Harvey will come into play, and if Spencer did see her bestie kill someone, that would certainly explain Alison’s hesitance to chat it up with Spence now.

What do you think Spencer’s secret is? Sound off in the comments below!

Catch the next episode of Pretty Little Liars on Tuesday, February 4, 2014 at 8 p.m. ET on ABC Family.

Kayti Burt is a contributing writer for Wetpaint Entertainment with a penchant for all things pop culture. Follow her on Twitter and Google+!