"The Godfather" is like "The Wizard of Oz"--one of those stories that have become so embedded in the culture that their dialogue and characters can be strewn through our conversations without explanation. We all know a Fredo, a Sonny, a Michael. When it comes to "The Godfather," we're all the experts.

The question is, experts in what? The Mario Puzo novel, the two movies he co-authored with director Francis Ford Coppola? (Forget the third movie, if you can.) When Random House hired novelist Mark Winegardner to write a sequel to the Puzo epic--the author gave his blessing to the project before he died--it seemed possible that the variances in the legend could be ironed out. Instead, "The Godfather Returns" trips over practically every discrepancy it encounters. In the first novel, young Vito's mother sends him to America. In "Godfather II," she's murdered on screen before he leaves Sicily. Winegardner splits the difference. He has her murdered, too, but by different means (a shotgun in the movie, a knife in the new novel). Tinkering with a cultural totem, Winegardner ties himself and his book in knots.

Winegardner's version picks up more or less where Puzo's novel left off and ends in the early '60s. There's new material about the presidential chances of a certain Irish-American senator, here named Shea. There's a dandy plot about Fredo's dream of moving all the graveyards out of New York City and over to New Jersey. There are a few great lines, the best being "The tiny-fingered Don started to cry." But Winegardner seems straitjacketed by the myth he inherited and at a loss when it comes to expanding it. Does it help to be told that Fredo's bisexual--who knows what Puzo would have made of that--or that Tom Hagen secretly longs to be a killer? C'mon, Mark, did you really think you could fool a Corleone fan with stories like that? Neither terrible nor original, this "Godfather" sleeps with the fishes.