Bobby [Kangana Ranaut] is a wealthy, enigmatic young woman living alone in Mumbai who works as a dubbing artist. In childhood, she intervened in a fight between her parents, an act that led to their deaths on a terrace. When a producer touches her at work, she reacts with brutal force, slicing his nose with a knife, and she is subsequently sent to an asylum. Her uncle manages her property and arranges for her house to be rented to a young married couple: Keshav [Rajkummar Rao] is the husband, and Reema [Amrita Puri] is his wife. Bobby becomes consumed by the couple, watching them from the shadows and stalking their every move.
Tragedy strikes when Reema dies in a kitchen fire caused by an exploding bottle of pesticide. Bobby grows convinced that Keshav is responsible and she presses the police for an investigation, though no evidence surfaces. She experiences terrifying visions of Keshav menacing her and even strikes out at him with a chair in front of the officers. The authorities deem her delusional, and she is sent back to the asylum. It is later revealed that her perception was distorted by her mind; during electric shock treatment, she recalls that she killed the wife not out of motive but because she believed there was a cockroach on her.
Two years pass. Bobby remains under medical care and largely confines herself to her house, until a London cousin arranges for her to be an understudy in a re-imagining of the Ramayana that she helps design. When she meets the cousin’s new husband, she discovers it is Keshav [Rajkummar Rao] again. He warns his wife that Bobby may be unstable, but his wife does not take him seriously. As Bobby immerses herself in the role of Sita, she begins to lose herself in the character and grows convinced that Keshav is Raavan, determined to be defeated. Concerned, Keshav reaches out to his old boyfriend, Varun [Hussain Dalal], who confirms that Bobby has a history of obsession and had once imagined him as a criminal. Varun breaks into Bobby’s house and uncovers boxes filled with photos that place Bobby into Keshav’s life as if she was his wife, not Reema. A photo of Keshav’s wedding to her cousin suggests that Bobby knew about their union far in advance.
Keshav confronts Bobby. The next morning, he tells his wife that Bobby tried to kiss him, while she informs his wife that he attempted to rape Bobby. Later, backstage, Bobby sees Keshav and, armed with an axe, pursues him, cutting a rope that causes a light to crash down. Fearful that she has harmed someone, she goes on the run and recruits three hallucinatory friends. They guide her to a library where she researches Keshav and begins to believe that he is a serial killer who takes on new identities and murders his wives. She returns to the house, dressed as Sita, and ties up her pregnant cousin when Keshav arrives, threatening him. Keshav tries to reason with her before revealing that he is indeed a serial killer. He even killed his first wife, a murder that occurred after Bobby had covered her in pesticide. Bobby fights back, and both she and her cousin are saved when Keshav is burned alive in the same manner as his victims. In the final moment, she strides down a London street, surrounded by her hallucinations, declaring with quiet resolve that she is exactly who she is and will not change.
