Erika Kohut, a piano professor in her late thirties at the Vienna Music Conservatory, lives a constrained life in an apartment with her overbearing elderly mother. Haunted by a past where her father had long been confined to a psychiatric asylum, Erika presents an exterior of aloofness and confidence. However, beneath this façade lies a deep-seated loneliness and sexual repression, which manifests in her unusual paraphilic interests, encompassing voyeurism, sadomasochism, and self-harm.
During a recital hosted by the Blonskij couple, Erika encounters Walter Klemmer, a young and aspiring engineer with a passion for piano and a sincere admiration for her skills in classical music. Their connection over favorite composers Robert Schumann and Franz Schubert is palpable, leading Walter to seek admission to the conservatory as her student. While Walter's audition impresses the faculty, Erika, visibly moved yet conflicted, votes against his acceptance, citing his differing interpretation of Schubert’s Andantino and questioning his intentions. Nevertheless, Walter’s talent prevails, and he becomes Erika’s pupil.
Meanwhile, another student, Anna Schober, grapples with her own anxiety driven by her ambitious mother. Consumed by jealousy after witnessing Anna and Walter socialize, Erika succumbs to a psychological break; she retreats to a coatroom and breaks a glass, concealing the shards in Anna's coat pocket. This act of sabotage results in Anna injuring her hand, ultimately barring her from performing in the upcoming jubilee concert.
The tension escalates when Walter seeks out Erika, leading to an intense encounter in a lavatory. After a passionate kiss, Erika exercises her dominance by humiliating Walter and orchestrates a sexual encounter that turns chaotic. Unable to conform to her specific demands to remain silent and focused on her, she commands him to await her letter regarding their future rendezvous.
As the conservatory dynamics shift, Erika feigns sympathy toward Anna's mother, proposing to take Anna's place in the concert with scarcely any notice. Walter, yearning for an intimate relationship, finds himself at odds with Erika’s desire for a masochistic connection. She presents him with a letter outlining her expectations and boundaries, but the contents repel him, forcing him to leave her room abruptly.
In a bid to apologize, Erika finds Walter at an ice rink, where an intense power dynamic unfolds as she submits to him in a janitorial closet. Their physical relationship begins, but Erika finds herself overwhelmed, unable to complete the act, leading her to a distressing moment of vomiting during their encounter.
When Walter later confronts Erika at her apartment, he violently forces himself upon her, disregarding her pleas for him to stop. The assault is the violent culmination of Erika’s complex psyche and desires, which she had previously hinted at through her letter.
As the tension culminates at the concert where she is to substitute for Anna, Erika's turmoil reaches a critical point. With a sharp kitchen knife discreetly hidden, she faces the audience. As Walter enters, jovial and carefree, the moment transforms. In a moment of profound despair, Erika deliberately stabs herself in the shoulder, allowing the knife to slip from her grasp as she exits the concert hall into the chaotic streets, a haunting image of both surrender and rebellion.
