Ethan Williams is a tormented man in his mid-30’s living on the outskirts of Melbourne. He begins grappling with vivid, haunting dreams that unveil fragments of his childhood, especially his connection to his mother. He remembers an obsession with having a bath; both a vessel of solace and a crucible of past transgressions. Ethan soon meets Kate, a woman from his local park, and becomes drawn to her, sensing a strange familiarity. Seeking clarity for his dreams, he consults psychologist Dr. Jessica Tobin, who believes these dreams could be repressed memories. During a date, Ethan invites Kate for a bath to help forge an intimate bond and deepen their connection. In the bath, overcome by disappointment in her true appearance, Ethan violently strangles Kate in a fit of rage and buries her body.

Six months later, Ethan transforms his appearance and continues seeking women to date, eventually meeting Briana, who is waiting for her sister at the park. Her sister's absence leads to Ethan accompanying her for a walk. Meanwhile, Dr. Tobin grows suspicious of Ethan's behaviour towards the women he has been dating. Whilst the connection between Ethan and Briana begins innocently enough, as their interactions deepen, Ethan's hidden darkness resurfaces after he notices a tattoo on her back that reveals a dissimilarity to his mother, leading to her murder.

Loren, Briana's younger sister, receives a phone call from a friend of Briana advising she has not heard from her in a few days and Loren grows concerned. Discovering messages linking Briana to Ethan, Loren investigates by visiting his home and uncovers the unsettling evidence of Ethan's actions. Further discovering a photo of his late mother, Angelique, Loren notices she bears a striking resemblance to this woman.

A bereaved Loren seeks help from Dan, a friend of her deceased father, to enact her own vendetta of justice for her murdered sister. Loren is visited by Detective Turner, who questions her about Briana's disappearance. Fueled by her own desire for retribution, Loren feigns ignorance, keeping her true intentions hidden. While planning her revenge, Loren changes her identity to help become intertwined with Ethan’s past, disguising herself to look similar to Ethan's deceased mother. Loren soon engages him in conversation in his local park and thus begins her game of psychological chess.

Through their following interactions, Loren uncovers Ethan's deeper vulnerabilities, emotions, and past. Ethan cuts ties with Dr. Tobin, feeling a sense of peace. Dr. Tobin, however, contacts the authorities, sensing the darkness lurking beneath Ethan's facade and believing he is a danger to society. Ethan and Loren spend the afternoon together and as the night progresses, a shared moment in a bathtub triggers a flashback that unveils the traumatic incident involving Ethan’s parents' death that shaped his life. In the present, Ethan and Loren grow intimate, with Loren surviving the bathtub encounter. Later in the night, Loren reveals her true identity to Ethan, exposing that Briana was her sister. She fatally wounds Ethan, and Detective Turner arrives on the scene, knocking at the door without answer. He investigates around the outside of the house until he finds himself in the dwelling underneath Ethan’s house.

In a post-credits scene, Loren cleans up the aftermath and takes off with Briana’s bracelet, leaving her with a sense of closure amidst the darkness. This scene shows that Detective Turner's arrival was not until days after the murder.