Giulio, Elio Germano, a film student, becomes obsessed with his striking neighbor Elisabetta Rocchetti and uses Fritz Lang films to anchor his thesis. He first catches sight of Sasha at the neighborhood video store, and the day she happens to be there, she is also trying to rent Alfred Hitchcock’s Strangers on a Train at the same time as Federica Chiara Conti. The two women strike up a tentative friendship, sharing a sense of secrecy and a willingness to discuss films as a way to navigate their own lives. The next morning, while Giulio rides his bike, he witnesses Sasha and Federica sharing a furtive conversation by a fountain, a moment that plants the seed of suspicion in his mind and nudges the plot toward a dangerous echo of the famous film they reference.
An intruder uses a key to enter Sasha’s apartment while her mother, Sasha Zerboni’s Milvia Marigliano, is at home, and Sasha’s mother is soon found dead with a brass pestle, a brutal and intimate murder that jolts the quiet building. The shock wakes Giulio to police questions and a public case that seems to orbit around his neighbor. He pores over the newspaper and learns that Sasha Zerboni was an only child and that her mother was a wealthy widow, a detail that deepens his fixation and pushes his suspicions toward a connection between Sasha and Federica. Back at home, his own mother, Elena Maria Bellini, voices concern about her new fiancé, a detail that quietly mirrors the larger theme of trust and deception threading through the two households.
As the investigation unfolds, Giulio discovers a bank statement showing almost 1 million euros in Sasha’s account, a clue that sharpens his belief that Sasha and Federica are involved in something darker than friendship. When Sasha returns, the cleaning crew chief informs her that Giulio had visited, injecting a sense of looming exposure into the already fragile web of relationships. Then a break-in at Giulio’s apartment—an intruder breaking an empty wine bottle and fleeing when Giulio wakes—raises the stakes and keeps the tension anchored in a real, present danger. To ease his nerves, Giulio invites Arianna Cristina Brondo to stay the night, and the two discuss the role of chance, games of fate, and the possibility that someone close to Federica could be drawn into a deadly scheme, a notion Arianna dismisses as paranoia even as the evidence begins to mount.
The next day, Andrea [Iván Morales], the video store clerk, tells Giulio that Sasha had been in and asked about him, hinting that she knew he watched her. Andrea’s later return to the store and his disappearance from the scene set in motion a chain of events that pulls Federica and her boss into the center of the mystery. When Andrea asks Giulio to mind the shop while he steps out, Giulio uses the opportunity to search Federica’s address on the store computer and follows her to her workplace, tracing the threads that connect Sasha, Federica, and the money at stake. Federica, leaving work with her boss, is revealed to be entangled in a coercive arrangement: the boss is blackmailing Federica for sexual favors tied to money she stole from a client, a detail that reframes the earlier suspicions around Sasha and Federica.
The peril escalates as Federica spots Giulio peering through a window and flees up a ledge, barely escaping a dangerous fall. Giulio fractures his ankle in the escape after sliding down a balcony, and the doctor confirms he will be in a cast for weeks. Arianna comes by to help him mend, and Giulio doubles down on his theory that Federica wants Sasha to kill her boss, though Arianna begs him to drop the dangerous speculation. The tension spikes when Andrea, visiting Giulio, tries to drown him in the tub; during the struggle, Giulio’s mother and her fiancé arrive, and the added chaos leads to Andrea’s fatal hit-and-run outside the apartment.
Sasha is taken into custody by the police, but the investigation continues to twist. Arianna, worried and curious, returns as the case takes a sharper turn: she spots a woman dressed in black approaching Sasha’s apartment, and Giulio realizes that Federica is the real killer. Andrea’s involvement becomes clear as part of a larger, complicating scheme, and the two men’s confrontation near the end of the sequence heightens the danger. Giulio calls the inspector, Edoardo Stoppa, who arrives at Sasha’s apartment just ahead of Arianna’s attempt to confront Federica. The chase leads to a rooftop confrontation, Federica slips from the edge, but the inspector keeps a firm grip and both he and Arianna manage to bring Federica to safety, placing her under arrest.
In the closing moments, Giulio’s cast is finally off, and a quiet postscript hints at new beginnings: his mother calls, and he learns of a fresh, unknowable possibility as a beautiful woman moves into Sasha’s former apartment. She sits almost naked on the sofa, reading a book—the Italian translation of The Window on the Night—unfazed by Giulio’s lingering gaze. The final image lingers on the notion that desire, danger, and the lure of close, watching eyes continue to shape a city where every neighbor could be a mirror, a threat, or a potential ally.
