Hard-boiled computer hacker Kidd and his sometime girlfriend LuEllen make for a refreshingly roguish couple. (She's a professional thief; he's a career criminal who paints and reads tarot cards.) But Kidd's fourth outing is a predictable political thriller that unsuccessfully tries to tap into post-9/11 paranoia. A hacker pal of Kidd's is brutally murdered, and his laptop with dirt on Washington politicos (and possibly Kidd himself) is missing. As he traces a link between the killer and a secret government organization with Orwellian plans, Kidd proves just as resourceful as Sandford's other popular hero, Lucas Davenport. But in ''Song,'' he lacks a story equal to his talents.