Terence McDonagh (Nicolas Cage) is a rogue cop fueled by drugs as he investigates the murder of a family of immigrants in Bad Lieutenant: Port of Call New Orleans. (FirstLook Studios)

German director Werner Herzog doesn't do normal. Over his lengthy career, he's captured a gallery of oddballs both real and fictional, turning his lens on everyone from a doomed Grizzly Man to Nosferatu to a crazed conquistadore (Aguirre, the Wrath of God).

He's finally met his match in manic actor Nicolas Cage, and the product of their unholy union, Bad Lieutenant: Port of Call New Orleans, should give fans of the cultish and weird a reason to cheer. Those seeking mainstream fare should consider themselves forewarned.

Bad Lieutenant: Port of Call New Orleans works best as a study of a man in the grip of madness.

Bad Lieutenant: Port of Call New Orleans begins with a shot of a fat, red-tinted snake, slithering through the murky waters left in Hurricane Katrina's wake while a cop named Terence McDonagh (Cage) is taking a swim. Diving into a flooded prison basement to save an inmate from drowning, McDonagh seems like a decent guy in spite of his cheap suit and cheaper talk. This bold rescue attempt gets him promoted to lieutenant but also saddles him with a back injury and a nasty Vicodin habit.

Working from a script by crime writer William Finkelstein, the movie initially plays like a by-the-numbers police procedural. McDonagh is assigned to a case of five murdered immigrants who are somehow linked to a drug dealer named Big Fate (Alvin "Xzibit" Joiner). But as the cop questions potential witnesses in cramped, rotting bungalows across New Orleans's Lower Ninth Ward neighbourhood, some of the filth rubs off. Soon, McDonagh is threatening suspects, smoking crack with others and wreaking havoc in a pharmacy, shouting, "Can I have my prescription, puh-lease?"

Bad Lieutenant: Port of Call New Orleans works best as a study of a man in the grip of madness. The film shares a name — and little else — with Abel Ferrara's 1992 picture Bad Lieutenant, which used a cop's moral disintegration as fodder for all kinds of Catholic hand-wringing. Herzog's film turns giddy when McDonagh's life and moral compass start to disintegrate. Along with his police work, the lieutenant must juggle an addicted prostitute girlfriend (Eva Mendes), a bookie (Brad Dourif), a key witness and his father's dog – tasks that prove increasingly tricky once he's beset by crack-induced hallucinations that involve some steely-eyed singing iguanas.

McDonagh's life is further complicated by his girlfriend, an addicted prostitute named Frankie (Eva Mendes). (FirstLook Studios)

The movie's finest moments come from Cage, who throws himself into this role with the energy of a man accepting a double dog dare. He does some of his best work in over a decade here – harassing a young couple in a speech he delivers as a disturbing, perverted aria or adopting an accent mid-film that approximates what Peter Lorre would sound like after a coke binge. Not all of it works, but it's a joy to see Cage take some risks again. He clearly relishes getting to elongate his vowels and contorting himself into a kind of crazed Quasimodo.

It's a shame, however, that Herzog never rises to the freakish heights Cage is going for. There are whole stretches of this overlong movie where it feels like the director is keeping his own lunacy in check. It was his idea to add those loopy iguanas, after all, but for every manic, surreal moment, there are countless other plodding, predictable crime-story elements – including interrogations, which he shoots with little visual flair. Herzog doesn't truly go for broke until the movie's mischievous final scenes, when he unleashes a genuinely surprising, throw-caution-to-the-wind conclusion that saves the entire film.

I'm still puzzling over what viewers are meant to take away from Bad Lieutenant: Port of Call New Orleans. The movie might be a freak auteur's sly comment on American corruption, a salute to beleaguered New Orleans residents who keep on keeping on or a prolonged answer to McDonagh's strung-out question "Do fish have dreams?" Only Herzog and his watchful reptiles know for sure — but they ain't singing.

Bad Lieutenant: Port of Call New Orleans opens Nov. 20.

Lee Ferguson writes about the arts for CBC News.