The cinematic journey unfolds in the vibrant heart of New York City, where a young waitress named Frances McCullen embarks on her usual subway commute. During this ride, she discovers an abandoned handbag that belongs to a French woman named Greta Hideg. Captivated by the unclaimed item, Frances takes it upon herself to locate its owner, leading her to Greta's address, which she finds eerily empty.
Sharing a cozy apartment with her close friend Erica Penn, Frances finds Erica increasingly intrigued by the handbag’s mysterious contents, as Frances keeps it in her possession. Their daily lives take a turn during a movie screening, a poignant reminder for Frances, as it conjures memories of her deceased mother. Complicating matters, her relationship with her father Chris McCullen has grown strained, as he buries himself in his work, leaving Frances feeling isolated.
After returning the handbag to Greta's home only to find it vacant, Frances encounters the enigmatic piano teacher, who invites her in for a friendly cup of coffee. During their conversation, Greta shares her personal stories, speaking of her lost husband and the mysterious whereabouts of her daughter Nicola, who allegedly resides in Paris. Feeling a sense of loneliness from Greta, Frances takes it upon herself to help by suggesting she get a dog. Though Greta declines, she later reaches out to Frances for help in acquiring a dog named Morten.
As days pass, their friendship blossoms, yet Erica grows increasingly wary of Greta, suspecting that Frances may be filling a void for a maternal figure. This tension culminates in shocking revelations when Frances discovers an unsettling secret in Greta's cabinets—numerous identical handbags containing familiar notes and phone numbers, including her own. Disturbed by these findings, Frances confides in Erica, and begins to set boundaries, declaring she wants to sever all ties with Greta.
Despite this, Greta's obsession with Frances intensifies, with her stalking behavior becoming more aggressive. Frances attempts to ignore her, but the police prove unhelpful, citing a lack of overt threats. As Frances tries to restore a sense of normalcy, she receives alarming images of Erica in dangerous situations, drawn into Greta's web of manipulation. In desperation, Frances and Erica seek legal protections by filing a restraining order.
Meanwhile, Frances’ concern for Morten grows, prompting her to investigate Greta's home for any leverage. What she uncovers raises more questions—a letter to Nicola indicates a discrepancy in Greta's story. Further inquiries reveal that Nicola has been deceased for four years, debunking Greta's façade as a caring mother.
As tensions heighten, the situation escalates with Greta's intrusive presence culminating at Frances's workplace. Even after police intervention, Greta remains relentless, emotionally tormenting Frances. When Frances attempts to confront Greta, ensuring her own safety, she faces chaotic outbursts from the disturbed woman, leading to a swift collapse of civility.
Seeking refuge, Frances temporarily relocates with her father but hope eludes her as she confronts her fears about Greta directly. In a moment of vulnerability, Greta embraces Frances, attempting to wrap her with a false sense of security.
The psychological assault reaches its peak when Frances unknowingly consumes a drugged drink, descending into confusion as she becomes trapped in Greta's control. Reeling from the effects, she finds herself confined within a toy chest, desperately yearning for freedom, hearing only Erica's distant voice as a flicker of hope.
As her captivity stretches on, days morph into a blur of mundane tasks under Greta's watch. However, desperation fuels Frances' instinct to fight back, leading to a violent clash, where she severs Greta's pinky with a rolling pin—her primal defiance sparking a fierce struggle for freedom.
The narrative weaves through unfolding horrors as Frances encounters disturbing realities, culminating in a face-off with unforeseen deaths and escapes. Detective Brian Cody becomes entangled in the sinister web as he dives into Greta's unsettling history, revealing her dark past of mistreating patients, which links back to her mysterious life in Hungary.
Through twists of fate, Frances desperately signals for help, leading to a chaotic confrontation. As the climax unfolds, Erica learns about Greta’s true nature, and together they devise a plan to neutralize their captor, overcoming her in a tense showdown that results in a daring escape.
Ultimately, the duo's fate hinges on their clever ingenuity as they confine Greta within the very toy chest that once symbolized their distresses, leaving an ominous atmosphere, aware of the small movements hinting at a future confrontation.
