Mona blathers at Hanna at length about how she never needed Caleb in the first place, and how poor boys are a hot commodity with diminishing returns, and how who even needs boys, and we should go glamping in each other's underwear, and I want to wear your body like a costume and go door to door being super weird and stalkery. Finally Hanna's like, "You didn't happen to accept a letter from Caleb on my behalf and then read it and then destroy it like a scary insane person, by any chance?" The whole point of this conversation is because Lucas is back in play for some reason, so he needs to overhear about the letter and realize that he's not alone in the Stalking Hanna Marin Club of which he is a founding member and acting secretary.
The four Liars corner Jenna in the bathroom and slowly reveal that all four of them are in there with her and that maybe they are going to beat her to death, but of course she just grins and acts smug and spooky and asks what the fuck they want. They explain the kindest possible way of looking at Jenna's molestation of Toby -- essentially that they weren't actually doing anything wrong, and Toby's problem with it was just Toby's problem; which is not without merit, but also don't coerce sex out of people -- and Jenna's like, "So you can see why I wanted that video where I blackmail my brother into fucking me." Yes, it is understandable that you would hire werewolves to infiltrate people's homes to get ahold of that kind of thing.
Jenna explains that the day before Alison disappeared, aka the day she got back from Hilton Head, Ali came to see her in the hospital. Sweet, right? Like, "Sorry I blew you up and now you're blind forever," right? No, this is Alison. She was there to say, "I know you're blind and all, but you can hear the audio of this video of you blackmailing your brother into fucking you okay. Or hey, can you hear it even better now that you're blind?" Jenna could hear it just fine, thanks.
Seems Alison's whole trip to Hilton Head was actually about getting this footage, including the Jenna Thing, away from the filmer of it and into a safe place. She made sure Jenna knew to stay out of Rosewood forever -- which is why she reappeared the day of the funeral, as the girls will figure out shortly -- and to never, ever accuse the Liars of blinding her that time she got blind, and whatever else. Insurance in every direction.