Los Angeles ? This is life in the 10 square miles where police Sgt. Sean Colomey works:

Laudelina Salazar Garcia, 39, the married mother of a 14-year-old daughter, was decorating her Christmas tree when a stray bullet fired from down the block passed through her front door — bullets whiz through the stucco walls of South Los Angeles bungalows — striking her in the neck. She died two days later. Police arrested two suspects, but prosecutors have decided not to press homicide charges because the men were returning fire from a drive-by shooter and are not criminally liable for a killing that occurred because they were acting in self-defense.

“I love it,” says Colomey of his job as he inserts his Crown Victoria into traffic on a mild, sunny, eventful afternoon patrolling the swath of South Los Angeles where most flat surfaces are marked with the spray-painted signs of the 60 or so gangs that deal drugs to customers and death to each other. Deciphering those signs — they change constantly, a public kaleidoscope of pervasive menace — is one of Colomey’s instincts, honed over 14 years in this police division. The signs assert territorial sovereignty. When one gang paints its sign over another’s, an experienced officer knows violence is coming.

Colomey pulls alongside a car in the opposite lane and asks one of the men in the front seat, “Where do you live?” The man, gesturing vaguely behind him, says, “Down there.” Colomey knows that someone with nothing to hide would give his address. The man goes on his way knowing the police are on the job.

The job in this police division includes patrolling five housing projects, one of them the largest west of the Mississippi. Each is an incubator of crime. In one, Colomey sees a drug dealer known as Ant talking on his Nextel. Nearby Colomey spots video cameras, the size of cigarette packs, tucked under the eaves of ramshackle houses to give occupants early warning of the approach of police or rival drug dealers.

Colomey races to a house where three gang units have converged. Officers have placed about a dozen men in handcuffs. Of the two who had guns, one was on parole, one on probation. Both are going to jail. What made the officers suspicious about the gathering at the house? The men are members of a gang that has a fresh grudge against another. And one man moved in a way that told the trained eye there was a gun in his waistband.

Colomey says that to produce an officer able to “work the gangs” requires about five years in a car — training the eyes, sensing the rhythms of the streets, recognizing who is the girlfriend of this or that gang member. An officer has to know when to shout to a young women walking by, “Hey, Charlene — how’s Luther?” and how to use the information when she says she is angry because Luther has been doing this or that.

Police Chief William Bratton speaks of the “peace dividend” the city would reap from rolling back the culture of tribalism celebrated by gangsta rap. The costs of each killing include emergency rooms, victim services, prosecutions, imprisonment. But at any time there are only about 180 patrol cars on the streets of this lightly policed, 480 square miles of city.

Colomey’s car takes him past a house emitting the smell of ether used in making PCP. He can start building a case for a warrant.

Past the garage where — more men in handcuffs; the man watching across the street is a murderer, but the prosecution’s chief witness disappeared — officers find shotgun shells and burn marks from manufacturing rock cocaine.

Past the place where an 8-year-old bled to death after being caught in the crossfire between gangs. Past the alley where five gang members set a teenage girl’s corpse on fire in front of her boyfriend’s house. She was associated by family with one gang but dated a boy from another, so after gang raping her they shot her in the head.

So, what is there for Colomey to love about his job? There is the company of his colleagues, and the satisfaction of being a brick in a thin blue seawall against a rising tide of chaos. His fellow officers’ minute-by-minute judgments, based on years of grim experiences, make life a little less hazardous for the many good people struggling to give their children escape velocity from the tightening gyre of gang membership, violence, drugs, incarceration and death.

George Will is a columnist for Washington Post Writers Group.