New York City plays a strong supporting role in most of Pete Hamill’s work, from the decades-long pub crawl remembered in “A Drinking Life” to his celebration of the man whose voice filled so many of those saloon hours in “Why Sinatra Matters.” His 10th novel, “North River” (Little, Brown; 341 pages, $25.99), digs deep into the hard details of the city’s life in 1934, five years buried under the Depression and at the beginning of the administration of Fiorello La Guardia.

The North River, the bygone phrase that gives Mr. Hamill’s novel its title, designates the Hudson along its busy stretch of shore from the Battery to the Midtown piers that berthed the trans-Atlantic steamships. Old time waterfront guys still used the term to distinguish the Hudson from the Delaware (or “South River”) when young Mr. Hamill first worked in newspapers in the early 1960s. It’s a credit to the author that nowhere in his novel does he jam an anachronistic explanation of the phrase into someone’s Depression-era mouth.

Dr. James Finbar Delaney is a 47-year-old former boxer and the son of a popular Tammany ward heeler named Big Jim. Delaney’s house calls as a general practitioner take him into the tenements of Chinatown, Little Italy, and the Irish families surrounding his block on Horatio Street. He meets Chinese prostitutes and Irish dockworkers on his rounds, which lend him a relative worldliness that transcends the clannishness of kin and neighborhood. Delaney’s Hippocratic oath and certain plot twists even compel him to treat the families of both sides in a mob war.

Mr. Hamill’s standard themes appear throughout: how immigrants learn about America through reading tabloids such as Mr. Hamill’s former employer, the Daily News, which appears as often in the text as the North River itself: “Rose was seated on her bed, back against the wall, her legs extended, big downy slippers on her feet, reading the Daily News and marking it with a red pencil.” At times he seems to sentimentalize the old neighborhoods, which close ranks and pull together only in the face of a legitimate outside danger — a mob threat against the doctor.

Serving a hard-luck clientele during a very rough time, Dr. Delaney seems uncommonly decent for a modern protagonist, but neither is he haughtily pure. His life proves that good works are sometimes rewarded, but also confirms Boss Tweed’s maxim, “Better to know the judge than know the law.” During his career of healing people, Delaney has built up a reservoir of goodwill from which to draw when he finally needs it: Knocko Carmody, the longshore union boss who protects him from a mobster named Frankie Botts, nearly lost his wife to peritonitis; another gangster, Eddie Corso, was saved twice by Delaney, on the battlefields of France and back home after a gangland shooting on New Year’s Eve.

The doctor is forced to call in favors after the birth of his grandson, who reintroduces vulnerability into Delaney’s life a year after the disappearance of his wife Molly. The child turns up in the doctor’s vestibule late at night during a New Year’s Eve blizzard, abandoned in his carriage with a flighty note from Delaney’s romantic, headstrong daughter. Nothing summons the joys and lurking dangers in the world like a helpless child. Through his sudden relationship with 3-year-old Carlos, the doctor is gradually restored from a grief-benumbed healer to a man who is fully alive, introducing his grandson to the wonders of snow, a shoeshine, a hot dog, and the Chrysler building. “The boy looked up and released a whoosh of astonished air.”

Delaney’s excursions around the city with young Carlos make a perfect vehicle for a historical tour of the city. If Delaney sometimes seems to have an especially encyclopedic knowledge of the layers of old New York, somehow gleaned from his doctor’s experience and from growing up a son of “Tammany University,” we’re almost as glad as Carlos is for the lesson.

When a young Sicilian woman arrives to help with the boy, an inevitable romance begins to grow between the caretaker and the doctor, but the truly memorable story in “North River” remains between the Delaney and Carlos. Although laid against the dark backdrop of the Depression, the pleasures of grandfathering have rarely been evoked as movingly as in this novel. The many dark, dangling side plots — of lost family, pushy G-men and mob rubouts — keep the book from collapsing into a smitten tale of doting sentiment. Frankie Botts’s gunmen may threaten the doctor’s new family, but the sharpest threat to the gift Delaney has received is the return of his wayward daughter.

Vladimir Nabokov once confessed that the main theme of his novel “Bend Sinister” was “the beating of Krug’s loving heart,” and that “it is for the sake of the pages about David and his father that it was written and should be read.” While certainly not the literary achievement of Nabokov, the most memorable and original passages of “North River” flow from the relationship between the doctor and his unexpected grandson. Clearly it is for the beating of Delaney’s heart that it was written and should be read.

Mr. Ward last wrote for these pages on the 1936 Olympics. His book,”The War for the Waterfront: Mike Johnson & the Mob” is forthcoming (Farrar, Straus & Giroux).