A hopeful little series debut introducing a mildly depressed 19th-century housewife and advice columnist who joins her husband on a Pinkerton case in hopes of being added to the payroll. And is. Horace and Sadie Greenstreet (he dashingly rolls cigarettes; she secretly smokes the butts) join one of the grand riverboats still surviving in 1873 to guard its owner, the aptly named Elcid Hardacre, who's received two death threats. But Hardacre is nevertheless found shot to death in his stateroom, and as the Mississippi Girl makes its stops from Cincinnati to Cairo, Missouri, the Greenstreets have ample chance (and the blessing of Cairo's Marshall Thurmond, an old pal of Horace's) to interview the suspects: Andrew DuBois, disgruntled since his offer for the Mississippi Girl was refused; Capt. McQuaid, disgruntled since he was fired; Sidney Cotton, the ship's doctor with gambling debts and a fondness for Nellie Dawes, chambermaid (later found poisoned); Culbertson, the ship's bursar; and Miss Atchison, seasick passenger with a taste for Whitman, as well as with accommodations too expensive for her wardrobe. The resolution involves false clues and multiple motives in the Golden Age tradition--and Sadie shines. With much wagered on period atmosphere (illustrations are promised Ö la Jack Finney's Time and Again), this excursion is sunk by almost affectless prose and wan characters. (How many Victorian careerwomen can the field absorb?) The invoking of a Mark Twainish nostalgia makes the reader all the more nostalgic for Mark Twain.