This idea came to me after reading Last Cask of Amontillado by Edgar Allen Poe. (Neither of them are related, just the revenge story got the gears spinning)

It had been years since he'd done anything to break my heart, that I knew of-of course. I feel though, as if he's hiding something. He's been gone for almost a week now, and I guess I must make due to entertain myself or find something to do. Maybe I could find something with some interest to me. After all, what could he be hiding from me?

"Big Mackintosh, I don't think ya understan'. I have some money now, we can save Appleblo-"

"Dammit Applejack, you don't get it. Applebloom is dead, she died last night, how many times are you gonna make me say it?" I heard him crying on the other line. The realization hit me as hard as a semi would hit a rabbit crossing the road. Head on it hit me. Almost crippled me up onto the floor.

"She can't be, I saw her two days ago, how can she-"

"She's gone Applejack, just come home. Please, I don't wanna lose you too. Just come home."

Applejack has moved on with her family from the farm to a smaller city farther east. After a chance encounter, little Applebloom over the years has developed a sickness few have survived from. When Applejack finds something that could change their lives forever she is dropped into a much bigger game that if she doesn't find a way out it could wind up killing everypony she knows.

Never in all my life have i questioned my very morals and ethics. There was... something more to those words they said in their last moments of life that made me think. Was what i was doing right? Or is this all a big mistake?

Cover art curtesy of Aaronbrony