Isabella is a half changeling that feeds on the love of others. She is also a master thief and has built quite a name for herself in Canterlot.
When something goes wrong on a heist, she has to flee from Canterlot, leaving behind all she has. She also learns she has matured farther as a changeling and now must obtain the love she feeds on directly from somepony, just like her changeling siblings. There's just one problem. She can't change form.