This story is a sequel to Change of Hearts
Derpy has always thought Spike the dragon was a good kid, if a little busy, but when she finds him sitting alone in Whitetail Wood looking glum, she finds out that, despite the fact that he doesn't mind "being a pony," so to speak, he still wonders what it would have been like to have known his real mother or father. Derpy does her best to cheer him up, but in the end, it becomes obvious that this particular question runs a little too deep for a wall-eyed delivery mare to answer -- for him or for Twilight Sparkle.
However, when chance lands an unusual old box in her hooves, marked "Return Service Requested," it sends her on a journey that results in her learning more about the matter than it was perhaps good for her to know -- or Spike or Twilight, for that matter.
Before it's over with, though, she encounters a looney band of traders, an addlepated old soldier, and yes, a big, purple dragon -- a very, very BIG, purple dragon.
That's when things get potentially lethal.
Cover art by Tarantad0 of Deviantart.