Repeat after me: A movie adaptation of a book is never going to be the same as the book.

For fans of Jonathan Lethem’s 1999 novel, “Motherless Brooklyn,” it’s imperative that they not only comprehend that thought, but also that they believe it. That’s not meant to take anything away from the script that Edward Norton based on it. Many of the book’s seeds remain in his film - which he also directed and stars in. But Norton has also given himself free rein to bring things in very different directions.

For instance, he’s added a new major plotline of his own, one that eventually takes center stage in the film. The book is mostly about the private eye protagonist and anti-hero Lionel Essrog (Norton) who, though plagued by Tourette Syndrome - which is conveyed through his verbal outbursts and physical tics - is working on a murder case. But the film opens things up to the extent that his case evolves into a story of illegal and morally corrupt and extremely racist urban renewal projects in New York.

Norton has also changed the time setting from the late-1990s to the mid-1950s. And though the film is period-perfect in its clothing styles and cars and other related items, it seems that he made this change mostly in order to give the film more of a noir feeling. But it’s a step he really didn’t need to take, and the noir side of things comes across as a little forced.

As, unfortunately, does most of the film. There are pacing problems. It starts off in a whiz bang manner, with some private eye business going very wrong (reducing someone who you’d expect to be a main character to a cameo role). But the excitement of the early scenes soon drifts off to a great deal of talking, and of introducing new characters, and of storylines getting off the ground but then going into unfocussed mode.

Sure, that last part is a main ingredient of some of the best noir films around (think of “Out of the Past,” “Touch of Evil,” “Double Indemnity”), but “Motherless Brooklyn” meanders too much, adding layer upon layer of different stories that might be related to each other, but also might not be.

There’s some very good acting here. Norton saddles his Lionel with enough Tourettic behavior, along with a dose of Obsessive Compulsive Disorder, to make dealing with others a challenge, but the affliction (the gimmick?) is never overdone. Gugu Mbatha-Raw’s portrayal of a political assistant and jazz lover and possible romantic interest is both shaded in gray and nuanced. To very positive effect, we’re never quite sure about who she is or about what she’s not sure about. There’s also an exceptional but brief piece of supporting work from Michael Kenneth Williams as a nameless trumpet player in a Harlem nightclub.

But the film’s two over-the-top performances don’t fare as well. Alec Baldwin’s Moses Randolph, who doesn’t appear in the book, and is based on the real-life New York developer Robert Moses, is a piece of nastiness from the moment he’s met. There’s zero nuance to him, rendering his character and his performance not very interesting. And Willem Dafoe, as Randolph’s do-gooder brother Paul, is far too intense in his “do-goodness.” His character and performance lean toward being annoying.

There’s no doubt that Norton had some great ideas for bringing the book to the screen, but there’s a sense that the project went out of control, that he was trying to do too much with it, that he couldn’t figure his way out of the complications that he set up. Everything is explained in the final 15 or 20 minutes, but so much is revealed, and done so in such a rush, there’s no way to understand it all.

Ed Symkus writes about movies for More Content Now. He can be reached at esymkus@rcn.com.

“Motherless Brooklyn”
Written and directed by Edward Norton
With Edward Norton, Gugu Mbatha-Raw, Alec Baldwin, Willem Dafoe, Bruce Willis
Rated R