On Pretty Little Liars Season 4, Episode 15 (“Love ShAck, Baby”), we got a little bit closer to the truth about what happened to Toby's mom, Marion Cavanaugh, while she was at Radley.

Assuming that Spencer's father was telling the truth — a big "if," but let's roll with it — then that means that someone else was on the roof with Marion when she fell. Someone else who happens to be a blonde. Someone that, perhaps, the truth about Marion's death was covered up to protect, for one reason or another.

So, who was the blonde in question? We've come up with a few theories to explore.

Alison DiLaurentis. Obviously, we can't discount that Ali could have had a short stay at Radley. Especially if we factor in the twin theory. One version of that theory is that Ali had a twin sister who pretended to be Ali for a while, while the real Ali was locked up in Radley.

Alison's Twin. On the other hand, if Ali does have a twin on the show, it's possible she's the one that was put away in Radley. Either case would explain why Spencer's dad was consulting with Ali's mom in the most recent episode (since we totally don't buy that it was really about her divorce).

Jessica DiLaurentis. We know that Jessica DiLaurentis and Peter Hastings were consulting about something in this episode. We also know that Jessica is pretty familiar with Radley. Is it possible it's because she was the patient on the roof the night Toby’s mom fell to her death? That would certainly be a twist, but we're not sure quite how it would fit with the rest of the mysteries.

CeCe Drake. The other most important mysterious blonde is CeCe. She's been shown to have a dangerous side, so we wouldn't be shocked if she was once in Radley. Though if that's the case, we're not sure who would have helped her cover it up. Maybe Ali got her family to help?

Sara Harvey. We're still not entirely sure why we were introduced to the concept of Sara Harvey, a girl from a nearby town who was a lot like Ali. Could she be connected to the larger mystery in some way? It seems like a longshot, but worth considering...

Who do you think was on the roof with Marion? Let us know in the comments below!

Catch the next episode of Pretty Little Liars Season 4 on Tuesday, January 21, 2013 at 8 p.m. ET on ABC Family.


Rebecca Martin is an Associate Editor at Wetpaint Entertainment and our resident Game of Thrones, Breaking Bad, and genre TV expert. Follow her on Twitter and Google+!