American couple Julia and Francis relocate to Bucharest, moving into an apartment building with a large picture window. Julia notices a man looming in a window from the building across the street. While Francis works long hours, Julia grows unnerved by the man in the window, who watches her on a daily basis.Julia's fear heightens when she learns of a serial killer, dubbed "the Spider" by local media, who is decapitating young women. While walking through the city one day, she senses a man is following her. She manages to flee from a nearby market but when Francis and Julia visit the market to review the security footage, it proves inconclusive.Julia befriends her neighbor, Irina. Irina shows Julia a pistol her boyfriend Cristian gave her for protection. Later that night, Julia waves at the man in the window, and he waves back. Convinced that it is the same man who followed her, she calls the police. Francis accompanies an officer to the adjacent building to speak with the man, whom they learn is named Daniel Weber.One day, Julia follows Daniel to a strip club, where he works as a janitor. Irina, a dancer at the club, spots her. Julia questions Irina about Daniel, but she knows nothing. That night, Julia hears a commotion in Irina's apartment. Julia convinces the landlady to unlock the apartment, but they find no sign of Irina. Francis believes Julia's fears are imagined, and points to the fact that "the Spider" has apparently been apprehended.The next day, Cristian arrives searching for Irina, who never returned home. They try to confront Daniel in his apartment but no one answers the door. Julia works up the nerve to knock by herself later, but it is answered by an elderly man. That night, a police officer arrives at their apartment accompanied by Daniel, who accuses Julia of stalking him. The officer chalks the incident up to a misunderstanding.Julia accompanies Francis to a company party, and gleans that he has made jokes about her fears to his coworkers. She angrily leaves and boards the subway, where she notices Daniel in the near-empty car. When he attempts to explain his voyeurism of her-that he lives an isolated, unexciting life caring for his father-Julia notices what appears to be the outline of a severed head in his shopping bag. She returns home, where she begins packing. She is interrupted by music playing in Irina's apartment. Inside, she finds Irina's headless corpse, before Daniel smothers her with a plastic bag.When Julia regains consciousness, Daniel recounts how he killed Irina and hid with her body when Julia and the landlady entered the apartment. Julia hears Francis enter their apartment next-door, but when she attempts to scream, Daniel slashes her throat. Francis calls Julia's cell phone, which he hears ringing inside Irina's apartment. He sees Daniel exiting and begins to walk toward Daniel, but Julia suddenly shoots Daniel multiple times with Irina's pistol, killing him. She steps out of Irina's apartment, covered in blood, and stares at Francis. (thanks to Wikipedia)