After moving into a quiet apartment, 24-year-old Elena begins seeing a woman standing across the street every night. At first, the woman simply watches her. Then Elena starts seeing her inside the apartment. The terrifying part? Nobody else can see her. Elena becomes obsessed with proving the woman exists, but the more she investigates, the more disturbing things she discovers-photographs of herself she doesn't remember taking, messages written in her own handwriting, and memories that seem to belong to someone else. Eventually, Elena realizes the woman isn't pretending to be real. Someone is pretending to be Elena.