One of the reasons novels are so hard to adapt into movies is because there’s just so much in them. Short stories are much easier to completely absorb into a two-hour film, but a book that runs several hundred pages? A real task. Often where filmmakers go wrong is in trying to cram as much of the novel onto the screen as possible, trying to please fans and make sure nothing important gets left out. In truth, that’s about the worst way to attempt an adaptation.

The best adaptations are ones where the filmmakers take the core of the novel and transport it onto the screen, maintaining the feel and ideas of the book, while jettisoning material that gets in the way. Having just read the novel on which it’s based I think the best example of that may be L.A. Confidential.

Directed by Curtis Hanson, who co-wrote the script along with Brian Helgeland, the film was critical lauded when it was released in 1997. Nominated for nine Oscars it won two, including for the screenplay (it lost best picture to Titanic – not a choice that aged well), which was adapted from the James Ellroy’s 1990 novel of the same name. It’s one of my favorite movies.

The book and movie both follow a trio of cops in 1950s Los Angeles as they try to unravel a conspiracy of corruption among the police, politicians, and wealthy businessmen. The events take place in the wake of “Bloody Christmas,” an actual LAPD prisoner abuse scandal, and are catalyzed by a (fictional, so far as I know) shotgun massacre of six people at a diner called the Nite Owl. Everything comes to a very bloody end.

The film tells a tight story, hewing close to the Nite Owl killing as the driving force and covering only a few days. The cops – Edmund Exley (Guy Pearce), Wendell “Bud” White (Russell Crowe), and Jack Vincennes (he who shall not be named) – each take their own paths to the truth, which is far from convenient for any of them. They boil down into fictional cop archetypes – the by-the-book choir boy who has to get his hands dirty (Exley), the thug who wants to be more cerebral (Bud), and the glib hustler enamored with Hollywood glitz and scandal (Jack). As someone else wrote a long time ago, Exley and Bud make one good cop between them.

The book, by contrast, spreads out over several years (with huge time jumps pretty clumsily handled) and adds to the Nite Owl a huge, sprawling murder case that involves torture porn and not one but two serial killers! I’m probably biased from having come to the film first, but this part of the book didn’t work that well for me, as it was so over the top it sacrificed some verisimilitude for spectacle. It is also dark as fuck, full of language that wouldn’t pass any modern PC filter.

What’s amazing is that for leaving out all that stuff the movie still basically ends in the same place in terms of theme. Exley learns that sometimes rules have to be bent to deal with real evil (the lesson of every good fictional cop and, sadly, way too many real life ones), while Bud does his best to rise above his brutality, but winds up reverting to type in the end. Jack winds up dead in both tellings, although for very different reasons.

What the book does that no movie can touch is get us much deeper into the heads of the three cops around whom the story revolves. Bud in the book is basically Bud from the movie, but the other two get backstories that really sharpen their characters. As in the movie, Exley is a war hero, but in the book we learn he’s also a fraud – he framed the aftermath of an act of cowardice to look like bravery. The relationship with his father – an ex-cop turned real estate developer – also gets a lot of development and helps explain why Exley is who he is. The Jack of the book gets a lot more development, including a tragic fuck up in his past and a love interest that gives him more of a potential redemption arc.

Which is to say some things are lost in the adaptation, but not much. For the most part, Hanson and Helgeland got it right on what to cut and what to emphasize. But don’t take my word for it:

Ellroy approved: ‘They preserved the basic integrity of the book and its main theme, which is that everything in Los Angeles during this era of boosterism and yahooism was two-sided and two-faced and put out for cosmetic purposes. The script is very much about the [characters’] evolution as men and their lives of duress. Brian and Curtis took a work of fiction that had eight plotlines, reduced those to three, and retained the dramatic force of three men working out their destiny. I’ve long held that hard-boiled crime fiction is the history of bad white men doing bad things in the name of authority. They stated that case plain.’

That puts Ellroy in a pretty limited company of authors who are fans of the movies based on their works. Like I said – sometimes it’s not about what’s left in, but what’s left out that makes an adaptation successful.