Jack Mosley is one of those cops we all know from the movies: old, tired, and cynical, with a bad leg and a worse drinking problem. The guy is mentally beaten and physically haggard, and if you saw him sitting on a park bench, you’d probably steer clear. There’s no doubt you’d steer clear in the office—if you weren’t in custody and all: While escorting a prisoner to court, Jack tells him that he believes “life is too long.”

Jack is played by Bruce Willis, who seems to have walked into 16 Blocks’ production straight from the set of Sin City. This walking mess of bad attitude, failing body, and deeply grooved face is ready to crawl under the nearest desk when his supervisor orders him to drive inmate Eddie Bunker (Mos Def) to a trial, which is, yes, 16 New York blocks away. After a few minutes of Eddie’s constant chatter, Jack needs his little helper—it may be 8 a.m., but the guy who once vowed to protect, serve, and actually obey the law needs to stop and get some booze. In a flash, there’s a man at Eddie’s window. And in another flash, the guy’s dead, shot by the cop who seconds ago was more concerned with the hair o’ the dog than with his prisoner.

Here, after that deliberately leisurely, unforgivingly hangdog opening sequence, begins 16 Blocks’ nearly real-time chase. Turns out that Eddie is supposed to testify against some dirty cops, including Jack’s longtime partner, Frank (David Morse). And this being a one-of-those-cops movie, Jack suddenly develops a conscience: Instead of letting the bad guys take Eddie down, he decides to go through a tremendous amount of derring-do to protect a kid who gets on his nerves even more than life itself.

The rest of the film’s 105 minutes are one long game of cat-and-mouse, with Lethal Weapon franchiser Richard Donner zipping the chase from bar to apartment to skyscraper rooftop as Jack and Eddie try to elude Frank and his crew. This, of course, is where the action-flick crowd will start to pay attention, as our heroes run up stairs and down, into the subway and out. If keeping the action fast and unrelenting makes for an exciting ride, well, it also makes for a rather unbelievable one. Picture even one New York City block between 8 and 10 in the morning. Now multiply the frenzy by 16 and try to figure out how the bad guys keep instantly finding each new nook the good guys tuck themselves into. Every. Single. Time.

But the characters are sharp and the dialogue is funny and you’ve been waiting a long, long time for Donner to make a half-decent movie again, so you forgive. More or less. Donner often zooms in on his cast members’ faces to let their peepers do the acting: Morse, squinty, is thoroughly evil; Def, wide-eyed, is terrified and, we’re convinced, reformed; Willis, haunted, could go either way, even after he seems committed to doing the right thing. Jack may be the central character here, but screenwriter Richard Wenk gives Eddie mouthfuls of lines that make him impossible to ignore—regardless of what standoff or dash into a hidey-hole is occurring at the moment. Eddie yaks pretty much the entire time, repeating like Rain Man how he has somewhere to be and something to do and throwing in the occasional philosophical musing or snappy one-liner.

Mos Def’s spin on Eddie, however, is the biggest Donner WTF? since Mel Gibson’s Lethal Weapon ’do. He gives Eddie a voice that’s squeaky, cartoonish, and, quite frankly, makes him sound as if he learned about those crooked cops while working at Tara. You’ll either hate it until the film ends or forget about it while concentrating on his otherwise terrific performance. (And the ease with which Wenk’s blather rolls off his tongue is remarkable regardless of—OK, in spite of—its tone.)

The aw-shucks goal Eddie dreams of pursuing after he’s freed, however—there’s just nothing good to say about that. (Hint: It involves flour.) Or about the fact that after all the gunfire, negotiations, and trickery Jack goes through to keep Eddie safe, Wenk gives us a twist that explains why Jack decided to start caring. (Hint: It involves treacle.) Does it make the least bit of sense? Let’s just say that if you accept Frank’s extraordinary hide-and-seek skills, you might buy it, too.