Credit: Eric McCandless/ABC Television Group © 2012 Disney Photo: Spencer and Melissa on Pretty Little Liars Season 2, Episode 21

We’re on pins and needles waiting to discover what exactly the secret is Spencer Hastings (Troian Bellisario) has been keeping from her besties on Pretty Little Liars. Rumor is, she has been keeping it for the entire series’ run. But just because the other Liars don’t know, doesn’t mean someone isn’t in on Spencer’s secret. Does Melissa know what Spencer is hiding?

Melissa was part of the N.A.T. Club. Melissa was one of the members of the N.A.T. Club, which means she was privy to many a secret in Rosewood. The N.A.T. Club basically made spying a hobby, gathering secrets – mostly in the form of video surveillance – on Rosewood residents. Was one of the secrets they gathered Spencer’s?

Melissa wants to protect her sister. This theory makes a lot of sense in that it explains why Melissa was so desperate to get the videos Alison stole back. Though it might not always seem like it, we actually believe that Melissa is trying to protect her baby sister. In this case, that meant getting back the videos from Ali – something she still seems to be trying to do.

It would explain their antagonism. We’re not saying Spencer doesn’t have other reasons to dislike her sister, but knowing that Melissa knows one of her deepest, darkest secrets (and something she is potentially ashamed of) would certainly make a compelling explanation for the tension between these two sisters. If Spencer’s secret does have something to do with their dismal relationship, we wonder how long Melissa has been keeping it. Or, more accurately, when Spencer did something she felt the need to keep hidden from her very best friends.

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