The roarin' '20's, the flamin' '20's the loose '20's -- now the jazzy '20's. In Muscatine, Idaho, there was a kid named Joe Geddes who was a natural with a sax. ""Little Gate"" the musicians called him. This is his story, this is the story of jazz, of the familiar names and familiar songs,- ""Dipper Mouth Blues,"" ""Sweet Sue,"" of Bessie Smith, Coleman Hawkins, of Chicago, New York, the ups and downs- and success. It is also the romance of Joe and Irene, blues singer from the right side of the tracks -- and it has a happy ending. But the important thing about this novel is the sense of authenticity in its background; it gives the reader understanding and sympathy with jazz, its leaders and their crews, the real dope on what they are after. Writing of this sort has to be a knack- there's a lingo all its own -- and it has to be good and flavorful. Amoral-well perhaps -- but in this book it seems all of a piece with the characters.