The movie begins with Jack Mosley (Bruce Willis) sitting in a bus, where he is recording a message to "Diane", and he says he wants her to know what really happened here, despite what the police might claim happened.

Jack is an alcoholic, burned-out NYPD detective. Back at the precinct house, after working all night guarding a crime scene, his Lieutenant gives him a simple assignment: escort a witness to the courthouse, which is 16 blocks away. The witness will be testifying in front of a grand jury, but the jury is set to be dismissed at 10 a.m., which gives them 118 minutes (almost two hours) to get to the courthouse.

The witness is Eddie Bunker (Mos Def), a chatterbox who quickly gets on Jack's nerves. A few blocks into the trip they get stuck in rush-hour traffic, so Jack hops out of the car and goes into a nearby liquor store, where he buys a bottle and takes a drink right in the store. Left in the back-seat of the car, Eddie can't believe what Jack is doing and is voicing his displeasure to no-one in particular when a man with a gun appears at the window. Instead of killing Eddie, he is shot dead by Jack, who is then shot at by the dead assailant's partner. Jack manages to get into his cruiser and run over the man who was shooting at him.

Jack and Eddie go to a nearby bar, one that Jack is familiar with. Jack kicks everybody out of the bar including the owner, then calls the station for backup. Jack's ex-partner, homicide detective Frank Nugent (David Morse) and several other cops come into the bar. Frank tries to get Jack to let him have Eddie, but Jack doesn't agree, sensing something isn't right with the situation. Frank explains to Jack that Eddie is about to testify against a (dirty) cop, who will in turn testify against many others to save himself. Frank takes Jack's gun away, and hands it to one of his guys. The gun gets wiped clean, and placed into Eddie's hand. Eddie is forced to fire a shot from Jack's gun, and is about to get executed when Jack takes the bar owner's double-barrel shotgun and shoots the cop (who was about to kill Eddie) in the legs. Jack takes Eddie and goes out the back door. Frank, really angry but still maintaining his poise, calls in more backups to find Jack and Eddie, claiming that Jack snapped and has started shooting at cops.

Jack and Eddie enter a nearby apartment, since Jack knows where the spare key is hidden. He goes to a bedroom closet to get a handgun. Frank knows that Jack's sister lives in the area, so he has one of his men check out the apartment. Jack is waiting for the cop and handcuffs him around a column and takes his cell phone/radio. When Frank finds out Jack has the cell phone he has Jack's position triangulated through the cellular system. Meanwhile, Eddie escapes and heads to the subway. Jack catches up to him and rescues him just before some of Frank's cops are able to catch Eddie.

Jack and Eddie are now in Chinatown, which is crowded with some sort of festival. Jack sees Frank in the distance and realizes that he must have used his phone to locate him, so he tosses it away and enters an old apartment building. Eddie keeps knocking on doors hoping someone will answer and let them hide inside; finally an old Asian man lets Jack and Eddie in his apartment. Frank's team searches for Jack and Eddie from floor to floor. In the apartment, Eddie changes clothes and tells Jack of his dream of opening a bakery. He carries a notebook everywhere with him consisting of all the recipes in the world for cakes, and he writes down everyone he meets birthday too. Jack calls the prosecuting attorney and explains the situation. She immediately sends escorts - more cops - to get them out safely, as Jack tells her the address and room number. Frank gets Jack's location from the mole and his men bust into the apartment, only to realize they've been duped by Jack. Jack walks down the stairs without obstacles now, only to be stopped by Frank, waiting at the bottom level. Jack had Eddie take a different route and Eddie is able to sneak up behind Frank and aim a gun at him. They head out the door and go to an underground sweatshop/kitchen/laundry room with Chinese immigrants running around.

Frank's men catch up to Jack and Eddie in the sweatshop and start shooting, Jack and Eddie manage to barricade themselves behind a steel door, only to find Frank waiting for them. Eddie and Jack are trapped between the door and Frank; the only escape is an elevator that isn't working. Jack and Frank trade shots while catching up on all the old memories they had. Frank tries to convince Jack that Eddie is a thief by listing all of Eddies prior convictions, which Eddie either denies or says he has changed, only to hear Jack tell him that people do not change. Just when they decide to open the steel door instead and shoot their way out, the elevator starts to work, and Jack and Eddie hop in and go up and out the front door.

Once they get out to the streets, they hop onto a bus and are chased after by two of Frank's men. They shoot the tires out and the bus loses control and spins out into a dead end. There are 31 passengers on the bus, so it has become a hostage situation. The SWAT team is mobilized, as well as the Commissioner and news crews. Jack asks the passengers to cover the bus windows up with newspapers, and tells the police that there are about 40 passengers. As they wait, Jack buys more time by demanding the prosecutor, a court stenographer, and a news crew be present before he will release the hostages. Eddie talks to a young girl, telling her not to be afraid, and that he will send her a beautiful birthday cake when that day comes.

Just when the SWAT team is about to break in, Jack releases all the passengers on the bus. Eddie sneaks off in the confusion, having switched outfits with another passenger. Jack remains on the bus, and believes that he has gotten his job done by getting Eddie out, figuring he could make his way the few remaining blocks to the courthouse in time. The cops still believe that there are nine more hostages, but the bus driver tells them that he was the last passenger and Jack is alone; that is when the SWAT team prepares to take Jack out, since they are told that he shot a few cops earlier. This is when Jack makes the tape that was part of the movie intro.

Eddie returns to the bus and yells for the cops not to shoot, and he gets back on the bus. Bringing up references to guys like Barry White and Chuck Berry, Eddie confronts Jack about him saying people don't change, and he wants Jack to believe that people do change. Jack fires up the bus and pulls out of the dead end. They are chased by the SWAT team, who keep breaking windows and firing shots and throwing flash and smoke grenades into the bus. The bus stops as it is wedged in an alley. When the SWAT team enters the bus, Jack and Eddie have already gotten out of the bus and into an adjacent building.

During the bus chase Eddie was shot in the stomach, Jack calls in help from his sister, Diane (Jenna Stern), who drives an ambulance and is a paramedic. She administers first aid to Eddie. As the ambulance pulls up to the courthouse, Frank pulls it over and orders Diane to open the rear doors, only to find nothing in there. Jack had Diane call another ambulance and put Eddie on it, which took Eddie away from the courthouse.

In the ambulance, Jack tells Eddie that he is a bad person, that Jack is one of the cops that Eddie was going to testify against. He is going to take full responsibility now. Jack asks Eddie to leave, and leave the trial to himself. Jack limps into the underground entrance of the courthouse and runs into Frank, who is always one step ahead of Jack.

• Bruce Willis - Detective Jack Mosley
• Mos Def - Eddie Bunker
• David Morse - Detective Frank Nugent
• Jenna Stern - Diane Mosley
• Casey Sander - Captain Dan Gruber
• Jeffrey Kelly - Detective Holland