Who Killed Madame President? : FICTION : THE ANNIVERSARY,<i> By Rachel Cannon (Random House: $23; 255 pp.)</i>

Melanie Lombard is the first woman to do the heretofore impossible: become elected president of the United States. But three days into the job, while America is still floating on a tide of good feeling that surrounds her landmark election, she is assassinated. By a woman, no less. And the loss of what promises to be an exuberant, youth-oriented, boat-rocking presidency (sound familiar?) comes to an abrupt end, plunging the nation, and Lombard’s best friend, Nora Whitney, into a slough of angst and despair.

Life goes on. The new president, a good-looking, well-intentioned but lackluster man named Dan Court, tries to make his own mark through a series of ineffectual legislative compromises that the more aggressive Lombard never would have countenanced. Whitney returns to Los Angeles and her job as an executive vice president of an educational software design firm. Melanie Lombard’s vision of an environmentally responsible, socially sensitive, fiscally sound America is fast fading.

Then, almost exactly a year after Lombard’s assassination, two things happen. Dan Court grows a backbone overnight and decides to go for broke by resurrecting one of Lombard’s most cherished agendas, a revolutionary environmental bill. And concurrently, David Weinhardt, a writer known for his insightful biographies of famous people, has decided to add Lombard to his list of illustrious subjects. He has begun to question Lombard’s friends, family and colleagues in an effort to draw a more precise, three-dimensional picture of the slain president. In reluctantly cooperating with Weinhardt’s wish to interview her, Whitney finds herself reexamining who Melanie Lombard really was, the depth of their friendship and the price maintaining it had cost her.

Whitney is a member of an elite sorority of feminist sleuths. Like Sara Peretsky’s V. I. Warshawsky, Sue Grafton’s Kinsey Millhone and Patricia Cornwell’s edgy Kay Scarpetta, she possesses above-average intelligence tempered with a weary cynicism. But at almost 48, Nora is a good decade older than most of her fictional counterparts. Perhaps because of that, she has no need for the gut-level, 180-degree contrariness that marks so much of V. I.’s and Kinsey’s movement through life. Her one serious love affair 20 years ago left her so gunshy that she is romantically dysfunctional. With the tantalizing possibility of a mature romantic relationship finally dangling within her reach, Nora has only just begun to admit to herself how walled off she has become: “. . . at the very core of [my] aloneness is the stark knowledge of how and why I came to be this way; I see myself as an architect of a life that may have missed the point.”

Although Nora has steadfastly managed to avoid domestic bliss and child-bearing, she has been an admirable surrogate mother to Melanie Lombard’s only child, Benjamin. So much so that when she asks Lombard’s widower, Hank Cochran, for permission to gingerly inform Bennie that the image of his mother that Weinhardt is unearthing may differ substantially from the prevailing hagiography, Cochran grudgingly agrees by pointing out, “You’re as much his parent as I am.”

Rachel Cannon’s first mystery doesn’t explode across the reader’s consciousness; it won’t grab you by the back of the neck the way April Smith’s “North of Montana” did. But you do find yourself wanting to solve the riddle of who Melanie Lombard is as much as Whitney wants to discover who really killed her best friend and who now is intent on killing her as well. And why.

. And we discover that the ghost that has haunted Whitney all her adult life, the specter of a perfect, supremely confident Melanie Lombard, may have been created more by the people who loved Lombard (and their own insecurities) than anything else.

Cannon’s characters are well-rounded and sound real. Her minimalist description of Los Angeles sounds like the verbal pictures a lot of us residents draw: It’s not paradise, but the city has its moments. If there is any disappointment in “The Anniversary,” it would be Cannon’s reliance on a cliche for the book’s villains; devotees of Rush Limbaugh et al will cackle, “‘I told you so!” when the bad guys’ identities are finally revealed.

That aside, Cannon has given us a heroine worthy of following through a series. By the end of “The Anniversary,” Nora Whitney has made some decisions about what’s important and worth holding onto in life--and what needs, finally, to be let go.