Accident was once just a cuddly little pegasus filly, confined to an attic by her parents for having abnormally large wings and being born the wrong subspecies. After being abandoned in the middle of Canterlot not long after her fifth birthday, she is adopted by the city's most capable burglar, who promises to train her to survive on the streets. Through it all, they learn to love each other, with all manner of adventures both funny and adorable along the way, and a sisterhood stronger than any of the two ponies' real family ties forms between them.

Of course, this meeting just happens to occur as an ambitious new guard with a vendetta against burglars attains the rank of lieutenant, a guard who may be more closely related to the two sisters than either of them suspect...

Thanks to hell00001 for his fine editing work!