Hélène Durrieux is introduced as the seemingly kind neighbor and a maternal friend to the three sisters at the center of the story. This facade of trust is shattered when the sisters discover she has been playing a deceptive and dangerous game for years, ultimately revealing herself to be a central antagonist. Her primary motivation is a volatile mix of financial desperation and a thirst for vengeance. She was involved in a shadowy criminal network that dealt in stolen art, and her life was threatened by this network after a fire led to the loss of valuable paintings she was responsible for, forcing her to repay the debt. This personal ruin fuels her actions, and she blames the sisters' father and an art collector named Christian Dalembert for her predicament, holding Dalembert responsible for taking the paintings and thus contributing to her downfall.

Hélène's role in the story is that of a ruthless manipulator and blackmailer. She holds crucial information about the disappearance of the sisters' father, having been the reason for his sudden vanishing. The sisters, who have been operating as art thieves under the name Cat's Eyes, are left deeply shocked after reviewing audio and video evidence that exposes her true nature. Hélène uses her knowledge of their secret identity as leverage, directly threatening to report them to the police if they do not comply with her demands. She forces them to steal a collection of paintings from Dalembert, framing it as a means for her to get revenge and recoup her losses. Her cruelty extends beyond simple blackmail; she escalates the situation by revealing that she has had the sisters' father captured and is holding him hostage, offering to return him only in exchange for the recovered paintings.

Key relationships define Hélène's interactions with the main characters. Her most significant connection is to the sisters, whom she initially approached as a trusted family friend and adult figure, making her ultimate betrayal all the more devastating. She had a professional and criminal relationship with the sisters' father, for whom she worked, using his talents as an art forger or dealer to sell stolen works until a falling out led to her orchestrating his disappearance. Her relationship with the art collector Christian Dalembert is one of bitter enmity, as she blames him for stealing what she considers her rightful property and sets out to use the sisters as her agents of vengeance against him. In terms of development, Hélène undergoes a stark transition from a kindly, maternal figure to a calculating, manipulative adversary driven by greed and a desire for payback. Her notable abilities lie not in physical prowess but in psychological manipulation and strategic coercion. Her primary weapons are information, blackmail, and the exploitation of personal bonds, as she expertly uses the sisters’ love for their father as a tool to control them and achieve her own selfish goals.