American couple Julia and Francis make the bold decision to move to Bucharest, settling into an apartment that boasts a large picture window. However, their new life takes a dark turn when Julia begins to see a man lurking in a window across the street. With Francis working long hours, Julia's anxiety escalates as the mysterious figure continues to watch her day in and day out.
Adding to her distress, local media report on a serial killer dubbed "the Spider," who brutally decapitates young women. One day, Julia becomes convinced that she is being followed while walking in the city. She manages to escape from a nearby market, but when they return to review the security footage with Francis, they find it offers no clarity.
In an attempt to regain her sense of safety, Julia befriends her neighbor, Irina, who reveals that her boyfriend, Cristian, gifted her a pistol for protection. That very night, Julia decides to wave at the man in the window, who shockingly waves back, further deepening her suspicions. Alarmed, she calls the police. When an officer accompanies Francis to talk to the man, they learn he is called Daniel Weber.
Determined to learn more, Julia follows Daniel to a strip club where he works as a janitor, only to be spotted by Irina, who works there as a dancer. Unfortunately, Irina knows nothing about Daniel. Later that night, Julia hears a strange noise from Irina's apartment and convinces the landlady to let her in, but they find no trace of her friend. Meanwhile, Francis tries to reassure Julia that her fears are unfounded, especially since “the Spider” has been caught.
The next day, Cristian shows up looking for Irina, who has mysteriously gone missing. They attempt to confront Daniel, but he doesn’t answer his door. Later on, Julia gathers the courage to knock, but is met only by an elderly man. That same night, a police officer arrives at their home with Daniel, who strangely accuses Julia of stalking him—a claim the officer dismisses as a misunderstanding.
Feeling isolated and dismissed, Julia joins Francis at a company party only to overhear him joking about her fears with his colleagues. Enraged, she storms out and boards a nearly empty subway train, where she is confronted by Daniel once more. He attempts to explain his odd behavior, claiming that he leads a dull life caring for his father. However, Julia notices something horrifying: the outline of what seems to be a severed head in his shopping bag.
Returning home in a panic, she is soon distracted by music coming from Irina's apartment. Upon entering, she makes a gruesome discovery—Irina’s headless corpse. Before she can react, Daniel smothers her with a plastic bag, knocking her unconscious. When Julia regains her senses, Daniel chillingly recounts how he murdered Irina and managed to hide when Julia and the landlady entered. Hearing Francis arrive next door, Julia tries to scream for help, but Daniel responds by slicing her throat.
Desperate, Francis calls Julia’s cell phone, the ringing of which echoes ominously from Irina’s apartment. He recognizes danger when he sees Daniel leaving but is met with shock as Julia, now covered in blood, emerges from the apartment wielding Irina’s pistol. In a frantic act of survival, she shoots Daniel multiple times, ultimately bringing an end to his terror. As the chaos unfolds, she locks eyes with Francis, leaving an unforgettable impression of horror and survival in the aftermath of their nightmarish encounter.
