Little is known of Cassie's backstory, least of all by herself. Brought up roughly on the streets of Paris, Cassie remembers a slew of half-brothers, second-cousins, and several distant uncles but none of her close family. Her street-family eked out a living as burglars, pickpockets and criminals for hire.
During the Universal Exposition of 1878, everything changed for Cassie. In the middle of a heist gone awry, Cassie eluded authorities by sneaking into the luggage of a group of English children visiting the expo. When she emerged, she discovered she was already onboard a boat bound for Dover. Once in London, her skills and guile quickly earned her a place in Willy Adams' cabal of hoodlums.