["Mignon"], James M. Cain's first novel in a decade, is nominally about the Civil War: period costumes aside, it barrels along like a private-eye escapade. Into New Orleans in the year 1864 comes Bill Cresap, invalided out of the Union Army and on the lookout for a stake. Before you can say Raymond Chandler, a Creole damsel in distress named Mignon Landry has appeared at Cresap's hotel room door, with a heartrending plea to get her daddy out of a military prison, where he has been sent for trading with the enemy. From this point on Mr. Cain never looks back, pulling onstage one gaudy character after another, including a sporting lady (gambling) who vies with Mignon for Cresap's heart—and involving one and all in some get-rich-quick trading in confiscated cotton. There's enough blood and lust in all this to satisfy the author's public. However, one nostalgic admirer...