Everyone knows that Mark Twain's

The Adventures of Huckleberry Finn

remains the great story from which, Hemingway roared, "all modern American literature" follows.

Also becoming a story of its own is Finn by Montgomery County's own Jon Clinch, a hot first novel that fleshes out Huck's nasty father, "Pap" Finn, and gives Huck a black mother.

Auctioned in January 2006 for an advance in the "mid six figures," and promoted by Random House as its lead fiction title this season, it's grabbing the reviews first novelists dream of.

Bob Minzesheimer of USA Today called it "a triumph of imagination and graceful writing." Jennifer Reese of Entertainment Weekly thought it "ravishing." Ron Charles of the Washington Post gushed that Clinch re-creates Finn "in a strikingly original way."

But if you want to hear a really inspirational tale, try this: Finn stands as the 52-year-old advertising veteran's sixth completed novel - just the first one published.

Clinch, who lives near the Lansdale exit on the Northeast Extension, understandably takes his reversal of fortune in good humor.

His first five novels, he explains, "didn't go anywhere." There was the "tragicomic whaling novel." And the "confession of the serial killer." And American Pantheon, which imagines "all the great American folk heroes," like Paul Bunyan and Pecos Bill, "still alive in America."

We'll stop there.

Clinch can't claim to be in the tradition of successful authors who received painful rejection slips. "More than 20 agents" declined to represent Clinch, so his manuscripts didn't make it to being turned down by New York houses.

"A very prominent New York agent," Clinch recalls without rancor, "told me that my stuff would never get published because what I write are historicals about men." Clinch thought, "But that's every book I love!"

From Upstate New York, where he graduated from Syracuse University in 1976, the bearded, affable author-to-be continued his love of classic American literature by teaching it for three years at Penn Ridge High School in Perkasie before switching to advertising.

He thus takes pleasure at the way reviewers are spotting echoes of Faulkner's Absalom! Absalom! in Finn, the sneaking into the plot of Melville's Benito Cereno.

The idea for Finn percolated in Clinch's head for decades. "That image of the floating house, the death house coming down the river with a body in it," he says, referring to a famous scene in Twain's novel, "was with me from when I was 10 or 12 years old, from when I first read Huck Finn."

"The other thing that kind of stuck with me," Clinch continues, "was the character of Pap himself. He represented things I didn't have in my life. I didn't know about child abuse and alcoholism and racism."

The decision to write the book came to Clinch at his Vermont vacation home in June 2005. "I was actually lying on our couch and my wife and daughter were over by the kitchen table, and I shouted to them, " 'Pap Finn!' They looked at me like, 'What's with that?' "

He grabbed Twain's novel, which he'd reread a couple of years before. It reminded him of all the strange stuff Huck finds in Pap's room. Clinch thought, "There's the story. . . . "

After he'd finished writing two-thirds of Finn, he became aware of Shelley Fisher Fishkin's study Was Huck Black?, which argues that African American voices influenced Huck's voice. The book bolstered Clinch's confidence that he could take Huck's blackness one step farther - it "legitimized the big risk."

The book took him only 51/2 months to write. As for Finn's publication history, it's an old story, updated for the Net age. He posted the opening two scenes of Finn on his Web site. A friend on a literary Net site he frequents, Backspace (bksp.org), told her agent, Jeff Kleinman, to read them. Kleinman offered to represent him, and the rest is breaking literary history.

One worry for Clinch was whether he'd be savaged by critics for using the N-word in his book (like Twain), and for the violence against blacks in it.

"I thought about it a lot," Clinch says. "I couldn't be true to the speech of Pap Finn or his coevals without using it." Still, he admits, when one of the most enthusiastic Random House backers of Finn turned out to be a black marketing director, he took comfort.

Clinch conceived Finn aware of the growing novelistic genre we might call Oliverism, as in, "Please, sir. I want more!" Writers from Sena Jeter Naslund (Ahab's Wife) to Geraldine Brooks (March, about the absent father in Louisa May Alcott's Little Women) have been going back to literary classics, filling in the blanks or writing prequels and sequels.

"I was thrilled when Brooks won the Pulitzer for March," Clinch admits, because he sees a high literary strain in the genre (e.g., John Gardner's Grendel) as well as a populist one (such as Ahab's Wife). He thought the prize brought "legitimacy."

Does someone need to read Twain's classic to enjoy Finn? "You don't need to know a thing about it," Clinch replies. "But I like to say that if you do read it, you will be rewarded. Because there are all kinds of tiny things you'll find. . . . "

Clinch acknowledges that, in the wake of Finn's success, he and his wife and business partner, Wendy, are watching their 18-year-old boutique ad shop (they're the only employees) "falling apart underneath my feet."

But he'd rather write novels. "I'm looking forward to adjusting the nature of my day," he says brightly.

Contact book critic Carlin Romano at 215-854-5615 or cromano@phillynews.com. Read his recent work at http://go.philly.com/carlinromano.