- "Being a pickpocket’s fine and all, but I got real potential."
- ―Cassandra Cain[src]
Targeted by Black Mask
Cass was a pickpocket within Gotham City and her activities resulted in her becoming the focus of a number of unsavory characters when she was arrested after unwittingly swallowing a stolen diamond that was the key to unlocking the fortune of the slaughtered Bertinelli Crime Family. Roman Sionis, the criminal kingpin who also went by the alias Black Mask, hired Harley Quinn to retrieve the diamond, but also put out a general reward of $500,000 for anyone who could bring Cain back to him alive.
Cass is soon arrested for thievery soon after leading Harley to raid the GCPD where Cass was still being held in custody. She is located by Harley and the pair escape, during which time Cass swallows the diamond for safekeeping. Harley learns of this and after their escape she handcuffs Cass to herself to prevent escape attempts. Cass is then then fed laxatives to hasten retrieval of the diamond. Cass and Harley initially interact with mutual suspicion, however the pair begin to warm to one another.
Cass is then taken back to Harley's flat where the two start to develop an affinity due to their (until then) solitary lives. The flat is then attacked by Huntress after Harley's landlord Doc gives up her location. Harley has a change of heart decides to make an arrangement with Sionis to give him Cass (and therefore the diamond) in return for his protection. Both parties agree to meet at an abandoned waterfront amusement park to make the switch. At the park Harley reveals to a distraught Cass of the deal and duct tapes her to a toilet, awaiting for the laxatives to kick in and the diamond to be excreted.
- "The inflection in your voice, the way you can’t hold eye contact, and the fact that you’re a filthy little thief, all suggest that you do."
- ―Harley Quinn to Cassandra Cain[src]
Cassandra is free-wheeling and fun-loving, but has become weighed down by the burdens of her family life. She turns to pick-pocketing to support herself, but doesn't quite realize at first the danger it places her in when she steals a valuable diamond. She quickly comes to idolize Harley Quinn when she breaks her out of jail, admiring her spirit. She is shocked when Harley betrays to her Black Mask, but eventually forgives her.
- Expert thief: She is a trained pickpocket, capable of using distraction and sleight-of-hand to fool people as she relieves them of her valuables. Though she has talent in committing the act, she isn't always quite so skilled at getting away when her victims soon realize that they've been robbed.
- Expert escapologist: Cain was able to uncuff herself from Harley Quinn without her realizing.
- Dynamite stick: Cassandra was handed this lit dynamite stick by Harley to throw at an assailant in a car.
- Handgun: Cassandra used Victor Zasz's handgun during a standoff.
- Hand grenade: Cassandra took this hand grenade from Harley's secret weapons cache.
- Bertinelli diamond: She unwittingly pick-pocketed and swallowed the Bertinelli Diamond, an extremely valuable diamond that was a key to unlocking the fortune of the Bertinelli Crime Family. Harley Quinn tried to get it out of her by heavily dosing her with laxatives, but there were those who were not so tender and were ready to cut it out of her.
- Birds of Prey
- Harley Quinn and Associates
- Harleen Quinzel/Harley Quinn - mentor
- Gotham City Police Department - Detainers
- Gotham City Hunters - attempted killers and captors
- Black Mask's criminal organization
- In DC Comics, Cassandra Cain is one of the world's greatest martial artists. She is the daughter of two assassins, bred to become the perfect killer, taught fighting since infancy and never learning to talk. She later rebelled against her parents, and became a vigilante under the alias Batgirl and later on Black Bat.