Mysterious and attractive heiress Abigail Clayton has not left her luxurious mid-town Manhattan loft apartment for almost two decades. The famous daughter of a wealthy industrialist, Abigail disappeared from the prying eyes of the press and the intrusiveness of her family on her 18th birthday, the day she received her massive inheritance. During years of self-imposed isolation, Abigail has had contact with only two people: her building's Concierge, Klandermann (Kevin Pollak), with whom she communicates via notes -- and Dr. Raymond Fontaine (Beau Bridges), a long-time family friend and her sole confidant for most of her life. When the death of her elderly neighbour prompts NYPD Homicide Detective Frank Giardello (Giovanni Ribisi) to launch an investigation, the agoraphobic Abigail is distressed to find him outside her door, asking to question her. Having tried to acquire the dead woman's now vacant apartment to ensure her privacy, Abigail is further upset when her requests go unanswered and new tenants, wealthy Lillian (Amy Smart) and Charlie (Jason Lee) move in. Abigail anxiously monitors her combative new neighbours from the safety of her front door's peephole, but her well-ordered world begins to unravel when she finally encounters Lillian and Charlie face-to-face-and her sheltered existence becomes threatened in unexpected and terrifying ways.