In the early 1970s, Dr. Henry West (William Mapother) founded the Atticus Institute in rural Pennsylvania, hoping to find evidence that proves supernatural abilities such as ESP are real.

The team is demoralized in their work by the time Judith Winstead (Rya Kihlstedt) is brought to the institute by her sister Margaret, who is troubled by her disturbing behavior.

Bizarre events begin to happen to the aides and their families outside of the institute, which they suspect Judith is somehow influencing, and many of them resign from their positions to escape from her.

Using methods such as electroshock therapy, the military try to tame the demon and force it to cooperate in exercises such as identifying the location of enemy bases, ignoring the effects these tests have on Judith.

The film concludes with a note revealing that Judith's body was buried in an undisclosed location following an autopsy, and her case "remains the only instance of possession officially recognized by the United States government".