So Edie gets the letter. We can see that it's addressed to "Edie Britt, 4362 Wisteria Lane, Eagle State, USA," so that solves that mystery: Fairview is located in the glorious state of Eagle, a state plentiful with lakes and an unusually elevated crime rate. (Why Susan chose to forego the name of the town in the address is still uncertain, though let's just give her the benny of the doubt and say she was subconsciously hoping the letter would get misdirected altogether.) Edie opens the envelope and unfolds the letter. At the top is the same "Dear Edie" we saw Susan pen back in the beginning of the episode, but then everything written below is in written in someone else's (a proud, proud PA, no doubt) completely different handwriting. It reads: "I don't even know how to begin this letter, but I'll start by asking that you please forgive me for what I'm about to tell you. I'd also like to emphasize that it's all Karl's fault. The truth is, I slept with Karl while you were still together. I know what I did was terrible. However, I did so after he told me he had broken up with you because he was in love with me. I know this letter may come as a shock..." It isn't exactly the most graceful letter, and Susan didn't do the greatest job of softening the blow, but I guess all the facts are there. But if the way Edie crumples up the envelop into a tight, tight fist is any indication, she isn't taking the news all that well.
Susan knocks on Mike's door. She's made him a "thank-you pie": "And by 'made,' I mean 'bought.'" He stands back to let her in, and she enters. From across the street, Edie emerges from the shadows, and she's looking icy mad and also hot in coat with a ginormous Cruela DeVil fur collar.
Cut to Edie opening Susan's garage and pouring gas all over Susan's house using a cute little watering can -- that's got to be the sweetest vehicle for arson ever used! Edie heads inside the house and douses the walls. Then she strikes a match. Bu...what about Julie? I'm guessing that, since she waited for Susan to leave, she probably did the same with Julie? Or maybe, when she was inside, she checked to make sure Julie wasn't home. I hope? I like Edie too much; I don't want to find out that she's secretly the sort of monster who would light a house without making sure it's uninhabited. Setting fire to all Julie's stuff is bad enough...
Back at Mike's, Susan is telling him, with unprecedented confidence, how glad she is that he saved her from Edie's wrath (ha), because it proves that he's still into her. Who is this person? Where is the needy Susan we know and...know? Huh. Maybe regaining Karl's love has given her a whole new alpha male outlook on life. Whatever it is, it's an improvement, so I'm not going to question it too closely. Susan points out that Mike's always trying to beat up her new boyfriends, and that he's always looking out for Julie and Susan, and you know what that all means. Mike: "That you're high-maintenance?" Ha! Susan tells him he can joke all he wants; she'll be the one to "break the ice." She tells him that she's "never stopped caring" for him. He asks about Karl, and she brushes that aside as a mistake that would have never happened if she'd thought there was the slightest chance with Mike. She comes around the table and feeds him a bite of pie: "I know you like pie. And I know you like me." Wow, hello, New Susan! She and Mike are just about to kiss when a suspicious yellow glow fills the room. Mike: "Your house is on fire!"