As a cab driver who is compelled to tell every passenger of his numerous conspiracy theories, from covert black helicopters to earthquake weapons in space to the real reason why the government puts fluoride in the water, Jerry Fletcher (Mel Gibson) seems on the surface to be just another frenetically eccentric element of New York's urban landscape. But there's a sense of urgency behind his obsession, and it seems to be tied into fragmented hallucinations that plague him. "It's on the tip of my brain," he often exclaims, heartbreakingly frustrated by his inability to recall that which is at the center of his paranoia.
   His one (reluctant) confidante is Alice Sutton (Julia Roberts), an employee of the Justice Department who has some of her own ghosts to haunt her. Jerry constantly bursts into her office to inform her of the latest conspiracy he thinks he's uncovered through his rigorous analysis of newspaper stories, which he meticulously cross-references to reveal imagined connections. Alice listens out of compassion, but doesn't believe a word of his wild stories. But, when some of his theories prove to be true, not even Jerry's most farfetched speculation could prepare him for the magnitude and danger of the plot he's stumbled upon. After publishing his hypotheses in a typewritten newsletter he produces, he finds his life endangered by the people he's inadvertently exposed (albeit only to his five subscribers, all of whom are murdered within 24 hours).
   Gibson is admirably up to the task of portraying the complexly layered character of Jerry, who is alternately tragic, hilarious, ingenious and heroic. Roberts is both strong and sympathetic as her character wrestles with conflicting emotions and instincts. As the malevolent Dr. Jonas, Patrick Stewart exudes pure cold evil. But several backstory elements could have been explained more clearly, and a more fully elucidated exposition of the truth would have increased the narrative's implications and thereby its tension. Still, even at two hours and 15 minutes, "Conspiracy Theory" is fast-paced and exciting, effectively mixing drama, comedy, ingenuity, suspense, revelation and a heartening sense of a triumph of humanity. Starring Mel Gibson, Julia Roberts and Patrick Stewart. Directed by Richard Donner. Written by Brian Helgeland. Produced by Joel Silver and Richard Donner. A Warner release. Suspense/thriller. Rated R for some violence. Running time: 135 min