Consider that ridiculous title. Though its poster and imdb entry eliminate the initial article, it appears onscreen as The Bad Lieutenant: Port of Call New Orleans. That's the bad lieutenant, not to be confused with Abel Ferrara's 1992 Bad Lieutenant, starring Harvey Keitel as a nameless New York City cop who gambles and grubs drugs until one harrowing case nudges him in a less wretched direction.

The bad lieutenant has a name: Terence McDonagh, and he's a police officer of similarly wobbly moral fiber. McDonagh's tale — inspired by Ferrara and scripted by William Finkelstein, but perhaps more important, filmed by Werner Herzog and interpreted by Nicolas Cage — opens with a snake slithering through a post-Hurricane Katrina flood. A prisoner has been forgotten in a basement jail. McDonagh and fellow cop Stevie Pruit (Val Kilmer) taunt the man, taking bets on how long it'll take him to drown in the rising waters. An act of cruelty seems all but certain until McDonagh, who's quickly been established as a righteous asshole, suddenly dives in for the rescue. Unpredictability, and quite a bit of instability, reigns thereafter.

A smidge of The Bad Lieutenant actually concerns police work, as McDonagh investigates the slaying of a Senegalese family. Everyone knows who did it, but there's no evidence, only a teenage eyewitness who's reluctant to testify against the neighborhood kingpin. But this is hardly a standard-issue procedural drama. Mostly it's a journey to the edge and back, multiple times, with an unhinged addict who prowls the streets of New Orleans "to the break of dawn, baby!" The storm-battered city provides an uneasy backdrop — this ain't The Big Easy (1986), and Herzog keeps his N'Awlins cliché-o-meter in check. He does allow for certain Herzogian indulgences, like an extended close-up of an iguana that may or may not be the product of McDonagh's drug-frazzled brain.

In a movie like The Bad Lieutenant, where every scene holds the possibility of careening to heights both campy and terrifying, Cage proves an inspired casting choice. Lately he's become more famous for his hair (which has its own Internet meme) and financial troubles than for his talents. His Oscar (for 1995's Leaving Las Vegas) capped years of cult success (1990's Wild at Heart), but after a brief late-'90s reign as action star and his success in the (lame) National Treasure films, he's kinda been off his game. Who, besides the people he owes money to, thought 2006's The Wicker Man was a good idea?

Basically Cage has nothing to lose, and his take on Lt. McDonagh is as haywire as it gets. McDonagh snorts coke before reporting to a crime scene; he threatens the elderly; he hauls his star teenage witness along when he confronts a john who's mistreated his prostitute girlfriend (Eva Mendes); he cackles like a maniac; he lurches around like a hunchback on crack. But he's not entirely monstrous — he cared enough to save that drowning convict, remember? Not knowing what McDonagh will do next is as entertaining as knowing it'll likely be completely insane. With Herzog behind the camera and Cage flailing in front of it, The Bad Lieutenant is the most fiendish movie of 2009. That's a recommendation.

THE BAD LIEUTENANT: PORT OF CALL NEW ORLEANS opens Fri/20 in Bay Area theaters.