Constance Brand was born the only child of Richard Brand, one of the richest real estate moguls in New York City and his socialite wife. The new child didn't fit into her parents plans, so Constance was raised by a series of butlers and maids. Not having her parents in her life, Constance acted out. She was always getting in fights at school, where she had no friends. Her parents kept trying to cover up her transgressions, but when she burned down the school killing at least 2 other students, they had no choice but to ship her to a private island.
There she was tended to by more of her parents servants, but these were so afraid of Constance they barely talked to her. One night she had enough and when the ship with the monthly supplies arrived, she attacks the captain and forces him to take her back to the mainland, and kills him anyway.
She then blackmails her father, and uses that money to get drunk and party. But all that stops when her mother dies. Her father calls her home and things look to get better between the two. Then her father meets a new woman with a daughter Constance's age, Gina. The two share the same love of destruction and become best friends then lovers.
The two vow to each other to turn their lives around. Constance gets a job at her father's company and cleans up her act, but Gina can't and overdoses one night. Constance's father blames her for the death of Gina, as does Gina's mother, who confronts Constance about it. Constance's kills her would be mother and goes back on the streets.
When things look the bleakest, Constance find an newspaper piece about Harley Quinn and starts to model her life after Harley. Things get better when Harley puts a call out for members to join her Gang of Harleys and Constance tries out. She is sucker punched in the dark and doesn't make the gang, so instead she decides to destroy Harley and her gang.
She turns her old private island in The Island of Horrible Death, changes her name to Harley Sinn and hires a private army full of mercenary and assassins she calls the Sinn-Dicate.
Major Story Arcs
Gang of Harleys
For more information see: Harley Quinn and Her Gang of Harleys
Harley Sinn, with the help of her Sinn-Dicate kidnaps Harley Quinn and takes her to their hid out in Red Hook. She then sends her best assassins to kill the Gang of Harleys while they are tending to their loved ones. Her plan quickly changes when she learns they will all be at Bolly Quinn's family restaurant. She has Edna blow up the building with the Gang inside while she forces Harley Quinn to watch.
Assuming the Gang dead, the assassins want to be paid, but Sinn learns her bank account is frozen so instead of paying them she murders them. She then takes an unconscious Harley Quin to her Island of Horrible Death. There she waits for Harley to make her escape and sicks her army on her.
Harley of course gets past them, with help of the Gang, who escaped being blown up, and confronts Sinn. Harley gives Sinn a deal, the pair would fight barehanded, if Sinn wins she could lead the Gang of Harleys. If Harley wins, Sinn would get mental help and then she could join the Gang. Sinn agrees but cheats and pulls a knife when it looks like she is beaten. Harley knocks her out with a choke hold.
Sinn wakes up in a hospital, where her father promises to get her help. A week later while being transferred from the hospital to a treatment center, she is rerouted to Arkham Asylum. Her father betrayed her, and what worse she became the obsession of the Joker.
For more information see: Harley Quinn #14 - Nether Regions
For more information see: Harley Quinn #17 - Red Meat
Blast from the Future
For more information see: Harley Quinn #20 - A Blast From the Future!