Martie Rhodes is a successful young computer games designer with a loving husband, Dusty, and a seemingly normal life. Her best friend, Susan, however, suffers from agoraphobia, or a fear of open spaces, and relies on Martie to take her to weekly therapy sessions. Suddenly and inexplicably, Martie herself begins exhibiting worrying signs of a mental disorder, fearing herself capable of inflicting great harm on her loved ones. At the same time, Dusty's brother Skeet also succumbs to irrational mental behavior and tries to throw himself from a roof. It soon becomes clear that these four characters are involved in something much more than a sinister coincidence.