DAVID FINCHER'S sixth feature, Zodiac, is also his most distinctly un-Fincher-like film. In one very brief montage, we see newsprint, numbers and figures floating over the screen, but that's about it. Even the opening titles—unlike the tense, jarring title sequences for Se7en and Panic Room—are simply ordinary. Instead, the film gets down to business, just like its subject matter. Zodiac concerns the real-life case of the Bay Area serial killer known only as Zodiac, who was at large for well over a decade, beginning in 1969.

The story flips back and forth between a San Francisco Chronicle reporter, Paul Avery (Robert Downey Jr.) and a political cartoonist for the same paper, Robert Graysmith (Jake Gyllenhaal), and a couple of local detectives assigned to the case, Inspector David Toschi (Mark Ruffalo) and Inspector William Armstrong (Anthony Edwards). Each pair does its own hunting for clues, such as decoding the killer's cryptic ciphers or checking for handwriting samples. Years later, Graysmith gets the idea to round up all the facts in one place and publish a book about the case. (It appeared in 1986.) Contrary to the ads, Zodiac isn't a horror film or a suspense thriller; it belongs to that unusual genre, the police procedural, which traces one seemingly banal clue to the next in the hope that something may pay off (it often doesn't). In that, Fincher's film is in good company with Akira Kurosawa's Stray Dog and High and Low, Alan J. Pakula's All the President's Men and Oliver Stone's JFK. Despite their lack of shootouts and chases, these films have a way of mesmerizing viewers who exercise a bit of patience, and Zodiac is no exception.

Fincher has gone out of his way to create an expert environment, with geographically and chronologically correct San Francisco landmarks. We witness the building of the Transamerica Pyramid, and characters sit through Don Siegel's 1971 Dirty Harry (the original Zodiac movie) at the now-defunct North Point Theater. Charismatic guest stars like celebrity lawyer Melvin Belli (Brian Cox) also turn up. The performances by the large and impressive cast—especially Ruffalo's—are superb, even if individual characterizations sometimes fade into the large tapestry. Gyllenhaal's Graysmith gets stuck with repeated references to his Boy Scout-like indifference to cigarettes and booze. And poor Chloë Sevigny, cast as Graysmith's wife, spends the film worrying and waiting and complaining about her husband's fanatical dedication to his work. (Sissy Spacek had the same problem in JFK.)

The film's most interesting aspect may also be its undoing. Zodiac is careful to point out just how ineffectual the Zodiac was as a killing machine. His victims added up to the tiniest fraction of homicides committed during his reigning years. In this, it asks the question: What fascinates us about this small-timer? But in asking, it also nullifies the question. It betrays the nature of obsession and thus separates itself from Graysmith. With his best film, Fight Club, Fincher delved headfirst into the maelstrom and chaos, swirling and celebrating with its every move. Zodiac is more of a passing fancy.

Zodiac (R; 158 min.), directed by David Fincher, written by James Vanderbilt, based on a book by Robert Graysmith, photographed by Harris Savides and starring Mark Ruffalo, and Robert Downey Jr., plays at selected theaters.

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