Set in 1928 at a boozy New York men's magazine called Bandbox, GQ contributor Mallon's madcap novel boasts a cast of characters that will look very familiar to media-world insiders. (Bandbox mogul Hi Oldcastle is presumably modeled on Conde Nast's S.I. Newhouse.) Boisterous Bandbox editor Jehoshaphat Harris, who recognizes that ''what he'd always had in huger measure than anyone else was nerve,'' is battling rival Cutaway's Jimmy Gordon, his erstwhile protege. Gordon has planted a spy among Harris' staff and a plagiarized story in Bandbox's pages. Already rococo, the plot goes seriously haywire when a naive Bandbox reader arrives from Indiana and is promptly kidnapped. Unraveling the mystery, and seeing which publication gets the scoop, is about as fulfilling as one of those subscription cards that falls out of this, or any other, magazine.