Five years after his last appearance (Murder in Paradise), Davey's Oxford don sleuth Ambrose Usher drops in (but mostly out of) a mystery so opinionated it might better have been a series of letters to the editors of the London Times. Depression economics, conglomerate ethics, IRA methodology, and world-class terrorism spawned by American gangsters are among the subjects crammed into this tractlike dialogue, which is intellectually interesting even if you can't imagine anyone actually saying it. The plot is typical Davey, overpopulated and overly complicated. Biographer Victoria McKenzie, recently jilted by a married chum of Usher's, is researching the life of Lord Cranford, fiercely successful top honcho of United Engineering International and recent purchaser of the staid publishing firm of Aston & Wren. Cranford would like a warts-and-all book-length obituary while he's still alive to read it, an idea too appalling to: Emilia, timidly Sapphic granddaughter of the founding Wren, who craves regaining the family firm; fight-hand man, Felix Morgan, a Viet vet with a suspicious ease at disarming letter bombs (aimed at Cranford); Warren Faversham, editorial director with a Blunt-like secret past that may be exposed by papers in Cranford's possession; an Irish actor co-starring with Cranford's wife in the manor house Festival production of Liaisons Dangereuses, the book's leitmotif. New Scotland Yard bumbles along, the FBI pays a call, and Usher flies off to M.I.T. in the middle of the night to unravel these intricacies on a megabrain computer. Two die and one is in the throes, but it's hard to care. Next time: more Usher, fewer economic sidebars.