When reviewing a book by Walter Mosley, it's hard not to simply quote all the great lines. There are so many of them. You want to share the pleasures of Mosley's jazz-inflected dialogue and the moody, descriptive passages reminiscent of Raymond Chandler at his best.

"Down the River Unto the Sea" is no exception. The book introduces cop-turned-P.I. Joe King Oliver. Oliver is just beginning to emerge from a decade-long funk after suffering at the hands of police gone bad. Locked up in Rikers Island following a phony rape charge, Oliver spent three months in solitary confinement and was so brutalized he nearly lost his mind. Now he avoids Brooklyn subway stations near his office on Montague Street because they feel like jail. Before Rikers, Oliver loved traditional jazz. Afterward, he gravitates to Thelonious Monk — dark, clamorous, discordant.

When the book opens, Oliver is out of jail and seeking help on two cases from a career criminal named Melquarth Frost. Frost, Mosley writes, "wasn't the kind of guy who told you anything unless it was either absolutely necessary or a lie." The retired bank robber and now clockmaker "knew quite a bit about evolution. He told [Oliver] that his greatest wish, when he was a child, was to change into something different; like wolves had become dogs or dinosaurs birds."

Mosley's densely populated novel is full of characters like Frost, many of them African American, who have struggled to rise above unlucky beginnings. Some, like Oliver himself, have more or less succeeded; others, like Leonard "Manny" Compton, have not. The black activist/journalist is on death row for the murder of two on-duty cops in what was a setup to keep him from uncovering a police-run drugs-and-prostitution racket. Oliver's efforts to save Manny require the kind of ruthless cunning he learned earlier from the rottenest of rotten cops.

Oliver's second case is his own. The woman who wrongly accused him of sexual assault has had a religious conversion and wants to atone, so Oliver thinks he sees a way to redeem himself with NYPD and maybe even return to the force. Not surprisingly, the two fraught situations intersect, and eventually Oliver is able to achieve some crude justice.

Along the way, there's a good bit of ugliness — Frost tortures a torturer to extract information — and close-up views of some of the seamier precincts of Manhattan, Brooklyn and Staten Island. For a while, Oliver is on the run from both cops and hoodlums and goes around with a shaved head and a fake mustache, and it's pretty funny.

Oliver is a lovely character, smart and decent like Mosley's popular Easy Rawlins, but also mentally fragile. He is haunted by a lifetime of encounters with savagery, some racist, some more ecumenical. His emotional moorings are in his relationship with his teenage daughter, Aja-Denise, (Oliver's bitter now-ex-wife refused to bail him out of Rikers) and with a circle of pals that includes Effy Stoller, a former prostitute Oliver protected after she killed her violent pimp.

Here is Mosley's introduction to melancholy, decent-hearted Effy: "Five three with fifteen pounds over what her physician would have called perfect weight, she had big lips and skin darker than mine. Her high, high heels might as well have been bare feet, she was so poised, and her hair had been done into the shape of a seashell that would exist in some far-flung future when humanity had devolved itself into geologic memory." Mosley, who is biracial and identifies as both black and Jewish, has a keen eye for his characters' skin tones, and the evident pleasure he takes in the human race's multiplicity of hues is infectious.

At 66, Mosley is, remarkably, as prolific as ever, sometimes producing more than a book a year. "Down the River Unto the Sea" — his 53rd book — is as gorgeous a novel as anything he's ever written. And with Joe King Oliver I'm betting, and hoping, he's given us a character we haven't see the last of.

Richard Lipez writes the Don Strachey PI novels under the name Richard Stevenson.

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down the river unto the sea

By Walter Mosley

Mulholland. 322 pp. $27.