For about half the time I spent watching Rampart, I assumed that it would suffice to tell you that it is a cop story written by James Ellroy (in collaboration with the film’s director, Oren Moverman). Ellroy has made a career writing about obsessed Los Angeles cops who live and work with a shifting relationship to what we call the law, and this film’s Dave Brown looked to be just another version of that sturdy model.

So too does the title seem to position it, if you understand it to refer to the Rampart scandal, in which 70 LA cops at the city’s Rampart division were implicated in all matter of egregious misconduct in the late 1990s. (It was the basis for TV’s “The Shield”,)

But while this story does take place in 1999 during the Rampart investigation, the title is, I think, used for its literal meaning of a defensive fortification. It is a character story of a man who lives behind a wall that he thinks protects him but actually destroys him.

Played by Woody Harrelson with a dental prosthetic that gives him a bit of a Bogart lisp and a lean frame that makes you worry for his health (in preparing for the role he got dieting advice from Christian Bale), Dave is a 24-year veteran of the LAPD. His cop moniker is “Date Rape Dave,” from a rumor that he killed a serial date rapist he was otherwise unable to arrest. That he still wears a uniform is a clue to his career. He came to the force after service in Viet Nam, and regrets that it is no longer “a glorious soldier’s department.”

But for all his bluster and brutality, Dave lives in a world of women. He married sisters, one after the other, had a daughter with each, and lives with all of them without realizing that they barely tolerate him. He indulges in one night stands with women attracted to his bad boy glamour but can’t connect with them. And his chief nemesis is a female district attorney who makes a point of pulling his carpet of bullshit out from underneath him.

Oren Moverman also directed Harrelson in The Messanger, as a military officer whose job is reporting the deaths of soldiers to their families. Once again he gets a strong performance out of him that brings you to sympathize with him in ways you won’t expect. And he sets him with a surprisingly strong supporting cast that includes Ben Foster, Sigourney Weaver, Robin Wright, Ned Beatty, Steve Buscemi, Anne Heche, Audra McDonald, and Ice Cube.

It’s not an unqualified success. There are a few too many loose threads that puzzle us: is Dave simply paranoid, or is there a conspiracy to bring him down? And the descent into hell sequence featuring underground sex clubs is a groaning cliché. But see it for Harrelson’s performance: he may never become a mainstream star, but he’s an actor who gets better everytime he’s given a bit more rope to work with.

Watch the trailer for Rampart