Will a changeling, given the identity of a pony, continue in that vein? Or are we, in fact, more than the sum of our memories?
Lies and secrecy abound as Twilight attempts to expose the changeling impostor who has taken everything she knew. Or, maybe she's the changeling attempting to steal everything the real Twilight has ever known. Or maybe ...
The one thing any pony or changeling can know for certain is that this will not end well.

An act of unwarranted aggression collaboration from the horse-addled minds of Sunshine-Smiles and Fiddlebottoms.