Telly Paretta (JULIANNE MOORE) is a married book editor whose life was upended when her 9-year-old son Sam (CHRISTOPHER KOVALESKI) was killed in a plane crash fourteen months ago. Despite the loving support of her husband, Jim (ANTHONY EDWARDS), and regular sessions with therapist Dr. Jack Munce (GARY SINISE), Telly's world is filled with grief and loving memories of her dead son.
She becomes more distraught and unbalanced, however, when she thinks that Jim has begun systematically removing all evidence that their son ever existed, such as excising him from photographs and erasing old videotapes of him. To her shock and horror, both Jim and Jack inform her that Sam never existed and was just part of an imaginary life she concocted following a miscarriage.
Telly flees and goes to the only person she thinks will understand her plight, former NHL player turned alcoholic Ash Correll (DOMINIC WEST) whose daughter perished in the plane crash along with Sam and others. Yet, Ash states he never had a daughter, a point that only confuses and frustrates Telly even more, as she knows she can't be going crazy.
Ash calls the police, but when they arrive to get her, so does NSA agent Carl Dayton (ROBERT WISDOM). With earlier prompting from Telly, Ash suddenly remembers his daughter and helps Telly escape from the Feds. As the two then go on the run from those agents, local police Det. Anne Pope (ALFRE WOODARD) who's been called to the case by Jim, and others including a strange man (LINUS ROACHE) who's always lurking about, Telly is determined to find out who or what's behind the apparent conspiracy designed to make her think her son never existed.