This is the hook that first pulls you into Presumed Innocent, which Frank Pierson and director Alan J. Pakula have adapted from Scott Turow’s best seller. The movie, like the book, is something more than a simple whodunit: one man stands trial, but as the labyrinthine case widens to reveal an intricate network of municipal corruption, it seems the entire system of justice stands accused and is found wanting.

As a suspense thriller, “Presumed Innocent” is nothing if not ambitious, and in this bubblegum season it earns bonus points simply by offering us something tougher to chew on. Still, Scott Turow is hardly Dostoevsky, though it often seems Pakula would like him to be. Even at his best (“Klute,” “All the President’s Men”) Pakula has always had a somber sensibility; when he goes wrong (“Comes a Horseman,” “See You in the Morning”) he’s downright turgid. Perhaps the hemmed-in style of “Presumed Innocent” (magnified by Gordon Willis’s deliberately airless cinematography) is intended as a reflection of Rusty Sabich’s repressed, legalistic mind, but it tends to drain a lot of the fun out of the Machiavellian maneuvers and bureaucratic back-stabbings that fuel the plot. Fortunately, “Presumed Innocent” perks up once the trial gets started: the appearance of Paul Winfield’s no-nonsense judge helps enormously, and Raul Julia is slyly urbane as Rusty’s slick defense lawyer.

Pakula’s strong suit has always been his work with actors, and he’s got a lot of good ones at his disposal. Ford gives a smart, self-effacing performance as a man so tightly self-controlled you keep waiting for him to crack. Bonnie Bedelia, as his bitter, neglected wife, finds moments of nifty insinuation in her role. Sab Shimono, as the less than impartial coroner, “Painless” Kumagai, and Joe Grifasi as the sleazy prosecutor Tommy Molto give their scenes a fine comic edge. “Presumed Innocent” is a slow fuse of a movie. It never quite explodes with the resonance Pakula intends. It tries too hard to be “important.” But the story it tells is a good one, and once it’s got its hooks in you, there’s no turning away.