Jerry Fletcher (Gibson) is a paranoid New York cab driver who sees conspiracy theories everywhere, and reports them to a busy DA (Roberts), who he has a crush on. When one of his theories turns out to be right, they are both put in danger.
With some movies, it's hard not to have that creepy feeling you've been here before. Here's Mel Gibson indulging in the brand of mentally unhinged heroism perfected in all those Mad Max and Lethal Weapon movies. There's Julia Roberts as the lawyer with the lips of an angel and the uptake of a sloth, slowly realising all those paranoid fantasies are true, as in The Pelican Brief. And at the helm is Richard Donner, also of the Lethal series, who can probably direct star vehicle comedy thrillers in his sleep (indeed, that's the only acceptable explanation for Assassins) and clearly isn't interested in listening to a pitch unless a cadre of evil super-agents in black helicopters are after the heroes.
Jerry Fletcher (Gibson) is the epitome of an obsessive nutcase, a New York cab driver with the compulsion to purchase a copy of The Catcher In The Rye when he gets a panic attack, and whose hobby is compiling bizarre conspiracy theories which he then writes up in a loony newsletter. Alice Sutton (Roberts) is the Justice Department chick to whom Jerry takes his insane notions, setting up a relationship that see-saws unsettlingly between smart-talking romantic comedy and stalker-stalkee menace.
Given that it's established early on that Alice is the daughter of a mysteriously-murdered judge and Jerry's neuroses run a lot deeper than they seem, it's a certainty that there will indeed turn out to be a conspiracy to get the both of them. And with Stewart doing a Marathon Man act as the CIA psychiatrist, Dr. Jonas, with a needle of truth serum ready and, after his first encounter with Gibson, a half-bitten nose, it's not too much of a strain to figure out who'll be behind everything rotten in the plot.
Though it tries to be different, with hair's-breadth escapes that don't depend on implausible stunts or Bondian-scale explosions, Conspiracy Theory is an uneasy mix of laughs and thrills; suspense and soap. While Gibson makes something of a role that plays cleverly with his inability to be entirely likeable, Roberts is dragged along for the ride and does little but toss her hair and listen to garbled explanations. The script unwisely goes out of its way to identify its maguffin as "Manchurian Candidate stuff", reminding you how effective this could have been if it weren't too lazy to cap all its fake explanations with a satisfying real one.
It's reassuring that both director Richard Donner and Mel Gibson feel confident enough with mainstream popcorn to attempt a thriller as obtuse, cerebral and challenging as this.