Nancy Drew is dead and gone. Whodunit? Sue Grafton (''A'' Is for Alibi) and Sara Paretsky (Burn Marks) are the chief culprits. Over the past 10 years their mysteries, featuring tough, believable, female private eyes, have put to rest , a century's worth of lady-detective stereotypes. Grafton and Paretsky weren't the first to explore the hard-boiled possibilities for women. (There was Dorothy Uhnak in the '60s, Marcia Muller in the '70s.) And they're not out there alone anymore. But despite the mass-market success that often spoils mystery writers, Grafton and Paretsky are still way ahead of the pack, digging deeper with each new book and avoiding the pitfalls of formula and pretentiousness.
Grafton's scrappy Kinsey Millhone orphaned as a child, twice divorced, a cheerful, sloppy loner at 33 has always been a little wilder, a little funkier than Paretsky's V.I. Warshawski. Millhone makes ends meet by doing a few routine investigations, looking into fishy insurance claims, in exchange for office space at the headquarters of California Fidelity in ''Santa Theresa'' (Santa Barbara, more or less). But in ''H'' Is for Homicide this fairly cozy setup is endangered, thanks to the arrival of an uptight efficiency expert from the company's Palm Springs office. So Millhone, under pressure to produce quick results, goes all out to uncover a bit of insurance fraud and winds up in the middle of a grand-scale crime.
Millhone has decided to investigate a car-accident claim filed by one Bibianna Diaz. Ms. Diaz isn't easy to track down: Millhone has to don a disguise or two and lie a lot (something she's terrific at) before striking up the germ of a friendship with her quarry, who turns out to be young, sexy, and likably brash. But just as the two women are getting chummy, the plot careens into Elmore Leonard territory. Diaz is kidnapped, with Millhone in tow, and they both end up in the L.A. barrio lair of Raymond Maldonaldo, the twitching (he has Tourette's syndrome) kingpin of Southern California's biggest auto- insurance-fraud operation.
The explanation? Diaz, it seems, is the unwilling object of Maldonaldo's psychotic and potentially homicidal romantic obsession. Which means that Millhone is in an intriguing bind: She'd certainly like to save her own skin and get as far away as possible from Maldonaldo's dank apartment. On the other hand, she wants to protect Diaz and help her escape if she can. Furthermore, Millhone is eager to find the evidence to gut Maldonaldo's operation and to nail the man himself for the murder of a California Fidelity colleague.
Grafton makes the most of the thwarted-love melodrama here, building it to a searing climax. But there's dark comedy, too, especially when Millhone takes a ''crash'' course in what she refers to as ''the Southern California College of Auto Fraud.'' And, in addition to being an incisively droll narrator, Millhone remains an unpredictable, more-than-just-engaging hero gutsy (or crazy) enough to talk back to a psychopath, vulnerable enough to slide into a sharp, touching reminiscence of homesickness at summer camp. So it doesn't matter much that there's no real mystery this time around. Even without a puzzle, Grafton keeps pulling out surprises and pulling us in. A