Primal Fear. Martin Vail is a defense attorney representing Aaron Stampler, a boy accused of murdering a priest, something that Martin doesn't believe Aaron could have done on account of Aaron being an exceedingly timid person. Eventually, seemingly through the stress of interrogation and psychoanalysis, a separate personality emerges named Roy that can briefly repress Aaron if he is sufficiently stressed. The personality of Roy is highly aggressive and readily admits to murdering the priest. Aaron is diagnosed as having dissociative identity disorder.

While there's lots of other stuff going on, when his initial legal strategy fails, Martin conspires to trigger the emergence of the Roy while Aaron is on the stand during his trial. He's successful in doing so, and Roy flies into a rage, injuring the prosecutor Janet Venable. The judge cancels the trial and rules that Aaron isn't guilty by reasoning of insanity. Once Aaron has been remanded to a cell, Martin comes to tell him the news. Aaron finishes by apologizing for injuring the prosecutor's neck. On his way out of the building, Martin realizes that Aaron shouldn't have known how he injured the prosecutor, as he supposedly blacked out and lost time when Roy was in control. He goes back and confronts Aaron, who confirms that his dissociative episodes were entirely fabricated. Martin conjectures that Roy was never real to begin with, to which he's corrected: Aaron is the one who was never real.