Melissa is still tearing through the house like a Pregnant Little Liar, looking for that ring. Spencer tries to leverage this because she's scared being alone in the house -- also so she can spy on Melissa, but mostly because she is actually more anxious than we've ever seen her.
Spencer: "Do you understand that I'm actually scared and being vulnerable right now?"
Melissa: "I can't help but assume that you are working an angle. I would not recognize you being scared or vulnerable if you printed out a label from that label-maker you asked for in second grade."
Spencer, verbatim: "I guess I'm just hoping that if it came down to it that you would protect me. Over someone who's not me."
Melissa: "You're talking in riddles!"
Spencer brings up a story of being bullied with jump ropes, back in the day. Apparently Melissa took the bitch down. Spencer would like some of that right now while their parents are out of town, in case the boob-puncher comes back.
Melissa: "I honestly don't remember this jump rope thing you're talking about. Also, I am pregnant with a devil baby, and my molester husband is a zombie right now. I got shit going on."
Spencer: "Somehow I'm a dick in this conversation? You are the worst."
Maybe it's Melissa that is the Jekyll & Hyde and Spencer's dream was trying to warn her that Melissa has two personalities and one of them is a killer of little girls. Like maybe she honestly doesn't remember that part of their childhood. Or any parts of their childhood. Or maybe the Jekyll of her took over back then with the jump rope and also took over again, with Alison, and that's why Ian said all that confusing stuff last year. When you think about how easy it would be for Spencer to turn into a serial murderer Melissa starts looking even more suspicious.
Or maybe Melissa totally does remember that whole deal, and just doesn't feel like admitting it because Spencer gets on her nerves.
Aria: "It's just so high school that the blind girl we blew up that time is now taking my Pottery class. What a bitch!"
Ezra, having recently showered: "Aria, you're still in high school. Don't take that away from me. Just make friends with her. You're both smart, pretty, wildly pretentious..."
Aria: "Ezra. We blew her up."
Ezra: "Work it out with Jenna. That's the grownup thing to do."
Aria: "Then I will most certainly be doing the opposite."