The new feature film, “Black and Blue,” seems to be based on a script hurriedly improvised on a hoary concept.

“Hey, do African-Americans accept Black cops?” is the question British screenwriter Peter A. Dowling’s script seems intended to answer. But director Deon Taylor’s movie only takes the idea as an opportunity for an urban chase film.

This means he won’t get much out of his good cast. Tyrese Gibson, known to us mostly from the “Fast and Furious” movies, has a decent turn here as the night man at a grocery store in an impoverished New Orleans neighborhood. London native Naomi Harris, who plays the lead here, appeared in “Moonlight,” “28 Days Later,” and the most recent Bond movies, where she plays Moneypenny.

In this case, she takes the cop part. West is a NOLA native who joined the Army when she was 17. After two tours in Afghanistan, she has recently joined the New Orleans Police Department. She and her partner, Kevin (TV specialist Reid Scott), come in from patrol and hear talk about an investigation into corruption in the force.

The rookie takes a second shift, putting back on her bullet-proof vest and body camera. And out she goes with an unfamiliar veteran who drives to a deserted power plant at the behest of someone who calls his cell phone. The older cop disappears inside.

Outside, she hears gunshots. She goes inside and is there in time to see and record the murder of a young civilian by an experienced undercover narcotics officer, probably Malone (Terry Grillo). Then the two narcs and West’s temporary partner see her. One of them shoots her.

She escapes them, bleeding from a wound that doesn’t make much sense given the configuration of her body armor. They want her video camera to protect themselves from arrest by the currently active Internal Affairs investigators.

But she remembers the neighborhood from her time there as a child. And she is helped, at first unwillingly, by Mouse (Gibson), brother of her old friend, Missy. Missy is now the moll of local drug king Darius (Mike Cole with gold caps on his upper teeth). It was one of Darius’ nephews that was shot at the power plant.

Malone works with Darius, splitting seized drug shipments with him. So the corrupt narcotics agent tells the employer of street dealers that fugitive West killed the nephew. Darius uses neighborhood residents’ cell phones to offer money for information leading to West’s capture.

Mouse’s nephew calls in her location. Mouse is also wounded a little. This forces him to take a dangerous route toward the sanctuary he and West seek in a nearby church. In the process of getting there, he is grabbed by Darius.

The perfidy of Kevin, the first fellow cop she calls for help, convinces her that there is no use seeking outside assistance. So she hides the body camera and walks right to the decaying apartment building where wealthy Darius has his headquarters.

In the end — spoiler alert — West uses a cranky, implausible version of the familiar “downloading evidence” routine to resolve the legal blame issue. A cliché rescue tops the movie off.

Now very simple stories can be made into successful movies. But even in “Rocky,” a mighty simple narrative, there is a parallel story about his girlfriend to take some of the pressure off the training sequences.

Here, there isn’t a second story. Mouse accompanies West so much that he doesn’t have his own story. And his acceptance of her as something more than just another police officer makes nonsense of this undigested movie’s central premise. If the audience can remember what it was.

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