Racetrack-betting lore is the primary asset in this leisurely mystery/melodrama--which never builds up much steam in its plot or much credible intensity in its character-tangles. The narrator is Lou ""Shifty"" Anderson, 38: professional magician (card-tricks a specialty), part-time horseplayer, and best friend of Jay Fox--the most fanatic professional handicapper at California's Del Mar track. And the complications begin when handsome loner Jay starts a hot affair with beach-acquaintance Marina, a classy French beauty (the guys call her ""the Princess"") who owns racehorses--courtesy of her estranged film-producer-hubby Dino, A few suspicious doings hover around Marina: a groom at her stables is murdered; she seems to be connected, too, to a high-stakes poker player who also turns up dead (after Shifty has helped to expose him as a cheater). Then, when Marina's most unpromising horse starts winning races with mysterious suddenness, things heat up a bit: Marina seduces Shifty (who has lusted for her), ensnaring him in her schemes--while Jay uncovers the secret of that horse's surprise-wins. And finally everybody joins shadily together, out to win big on the dark horse's next race. . . with predictably ironic results. Murray (The Sweet Ride, Malibu, etc.) seems unsure about almost everything here: whether to make Shifty or Jay the primary hero (neither one is fully engaging); whether to treat the plot as a mystery or a caper (the result is a shaky compromise). Half-heartedly developed, too, is a serious theme about the nature of the professional gambler's existence. But, if patchy as suspense and thin as romantic melodrama (especially when it gets earnest), this slickly written novel offers lively, diverting close-ups along the way--of handicapping techniques, neo-Runyonesque gamblers, and the laid-back beach/track subculture.