This is based off the song an Autumn night which was done by Bagpipe Brony or Psychgoth on youtube. Essentially it's about how Derpy gets a package to deliver from twilight who sends her off to deliver the package of reasons never explained. Derpy Approaches the manor and enters despite being warned before hand not to do so.

[youtube=http://www.youtube.com/watch?v=hKmh71mhyz8&feature=share&list=PL0uNGpfbUlvIwgUAed2xhULE5ASxupyyg]

This is the song the story is based off of.