When Twilight becomes determined to unravel the mystery of how poison joke does what it does, Fluttershy agrees to help since her reaction to the flower is the least debilitating among all their friends. Things don't go as planned, of course, and the experience changes Fluttershy and Twilight's lives in ways neither of them could ever have imagined.

This story is quite tame as far as the "Sex" and "Fetish" things go, but I figured I'd better rate it "Teen" and put the tags on just to be safe. Oh, and the cover image comes from Asssha on DeviantArt.