Harry Bosch has become Mariano Rivera. Like the great New York Yankees pitcher, the Los Angeles detective has become a closer.

If the poetry and grace of the national pastime, the recognition that baseball is a microcosm of life, has somehow eluded you, you may not know what a closer is. So I’ll tell you. When the pitcher who starts a game is finished, either because he’s tired or ineffective; and the other pitchers called in to replace him have all done their best; and the game is close in the last inning; it is the closer’s time to stride onto the field and slam the door on the opposing team.

The best in the game for nearly a decade, and probably the best ever, has been Mr. Rivera, the slim Panamanian who, when given the ball in the ninth inning and asked to protect the lead, has been almost as automatic as a sunset at the end of the day.

Hieronymous Bosch (Harry to pretty much everybody) retired from the L.A.P.D. three years ago, but in Michael Connelly’s wonderful new novel, “The Closers” (Little, Brown, 403 pages, $26.95), he’s back in a new job.

The newly named Open-Unsolved Unit (which seemed, from a public-relations point of view, a better name than the Cold Case Squad) handles crimes that remain unsolved after all apparent leads and clues have turned into blind alleys, and when fresh homicides, rapes, robberies, and other major crimes scream for attention.

It’s a prestigious assignment, the theory being that only the best detectives will be able to solve these apparently insoluable crimes years after the fact. As a colleague fervently puts it, “We’re the closers, baby. If you’re in homicide, this is the place to be.” In Los Angeles alone, there are about 8,000 unsolved major crimes, most of which gnaw at the guts of the cops who couldn’t bring the perps to justice.

Having been away for three years, Bosch is excited to be back in the familiar role of someone who can do some good, an avenger for those who can no longer defend themselves. “As he read through the catalogue of the city’s horrors,” Mr. Connelly writes:

Bosch felt a familiar power begin to take hold of him and move in his veins again. Only an hour back on the job and he was already chasing a killer. It didn’t matter how long ago the blood had fallen. There was a killer in the wind and Bosch was coming. Like the prodigal son returning, he knew he was back in his place now. He was baptized again in the waters of the one true church. The church of the blue religion. And he knew he would find his salvation in those who were long lost, that he would find it in these musty bibles where the dead lined up in columns and there were ghosts on every page.

The case he catches occurred in 1988. A 16-year-old girl was abducted from her bedroom, carried high up a hill behind her house, and killed. There were few clues, fewer suspects, and nothing of any substance. The police were unable to find a motive or anyone who wanted to harm her, and the search for the murderer soon ended.

The murdered girl was an only child, and the lives of her parents were taken away as completely as hers. Her father, once a successful restaurateur, fell quickly into a bottle and would be found years later on skid row, where he lived with hundreds of other hopeless, homeless alcoholics and drug abusers. Her mother kept her daughter’s room exactly as it was the day she was taken.

She lay on her daughter’s bed, tirelessly reading and rereading her daughter’s diary, calling it her bible. She had picnics on the spot where her daughter was found. When Harry calls on her for the first time, she answers the door in “a shapeless blue pullover dress that helped hide her own shapeless body. She wore flat sandals. Her hair was a color red that had too much orange in it. It looked like a home job that didn’t go as planned, but she either didn’t notice or didn’t care.”

Seeing the woman and hearing her plead with him to find her daughter’s killer gives added motivation to Harry and his partner, Kiz Rider, with whom he has worked closely before. As they investigate they find evidence of what seems at first to be sloppy police work, which irritates them. Then they discover it is something else, which enrages them.

As is true of all of Mr. Connelly’s work, “The Closers” is a paean to meticulous police work. What it lacks in action – there are, happily, no car chases or shootouts – it makes up for in straightforward, intelligent investigation. Dialogue is as realistic as it gets. It doesn’t have the originality of Elmore Leonard or the snappiness of Robert B. Parker, but then real people don’t talk like those authors’ characters – they talk like Mr. Connelly’s.

It was Harry Bosch, however, who helped make Mr. Connelly one of the most popular and critically hailed mystery writers in the world, and it’s not hard to see why. He is a thoroughly decent man, soft and compassionate, his heart breaking for the ruined lives of the ripple-effect victims of tragedies. But he’s not a weenie. When the murderer is finally caught, he asks Bosch to shoot him on the spot, to put him out of his misery. He even knows that Bosch despises him, saying, “You want to kill me, don’t you?”

“Yes,” Bosch replies. “I’d want to kill you. But that would be too good for you. You are going to have to pay for what you did to that girl and her family. And just putting you down right here wouldn’t even cover the interest on seventeen years.”

How could you not love the guy?

Mr. Penzler is the proprietor of the Mysterious Bookshop. He can be reached at openzler@nysun.com.