When Laurie King's editor Kate Miciak told her that the sales department at Bantam Books would love it if she could bring her two award-winning mystery series together, King remembers saying, "that's the most ridiculous thing I've ever heard; the whole thrusts of the two series are just incompatible." But King adds, "Kate knows me well. When she plants an impossible idea in my head, I won't ignore it."

At first glance, the two fictional worlds created by King could not be more dissimilar. The four novels featuring San Francisco homicide detective Kate Martinelli are police procedurals that combine grisly murders with astute portrayals of contemporary life. The eight Mary Russell novels, with the bookish, intelligent and underage woman who meets and marries Sherlock Holmes, are historical adventures of political intrigue and detection, set in exotic locales. But in just two weeks, King with an ingenious bit of plotting, figured out a way to graft her extensive knowledge of Arthur Conan Doyle and the Sherlock Holmes canon onto the gritty world of Kate Martinelli. The resulting book, The Art of Detection, will undoubtedly appeal to fans of both series.

In King's new novel, her 17th (in addition to the 13 series novels, King has written four standalone books), Kate Martinelli discovers what could be the original manuscript of an unpublished Sherlock Holmes novella while investigating the bizarre murder of an eccentric, obsessive Holmes collector named Philip Gilbert. King interweaves the contemporary mystery and the text of the novella, narrated by a British detective visiting San Francisco in 1924. The detective calls himself Sigerson (a well-known alias of Holmes, and unmistakably him, even those his name is never mentioned).

While the sales department at Bantam may love the idea of combining King's two series, the resulting novel is far from a marketing gimmick. The twin narratives of The Art of Detection are linked around the book's overarching theme of sexual identity. As Kate Martinelli discovers, the dead man's personal life was decidedly ambiguous, while Sigerson's investigation concerns the tragic consequences of a young Army officer's desire to acknowledge his transvestite lover. The result is a multilayered story that has a lot to say about the societal and cultural issues of homosexuality. And, of course, both narratives resonate with Kate Martinelli's own back story. As her fans already know, Kate's a lesbian. Deeply closeted in the first book of the series (A Grave Talent, St. Martin's, 1993), now she's "out," living in a committed relationship and raising a daughter in a funky San Francisco neighborhood.

When she first appeared in AGrave Talent (which won the Best First Novel Edgar Award), "it was absolutely believable that Kate would be a closeted cop," King says. "But in 2004, it made no sense whatsoever. The change in San Francisco in those 12 years has been extraordinary. Kate is a family woman now, pleased with herself, part of a community in ways that weren't possible before. And the fact that I could take the opportunity to track this story next to the consequences of coming out of the closet in the 1920s was really interesting."

The consequences of sexual preference represent a thought-provoking conceit for a genre novel, but the intellectual ambitions of King's books won't surprise her many fans. A Darker Place (Bantam, 1999), one of her standalones, is a carefully researched, vivid exploration of religious cults. In the last Kate Martinelli novel, Night Work(Bantam, 2000), King delved into radical feminism and bride burning. And several of the Mary Russell novels feature milieus from Palestine in 1919 (O Jerusalem, Bantam, 1999) to India in 1924 (The Game, Bantam 2004). Reading King is like going on tour with a learned professor who has a gift for storytelling.

King enjoys exploring ideas connected with religion and its cultural and literary roots. She has a B.A. in comparative religion from the University of California at Santa Cruz (a native Californian, King now lives about 90 miles south of San Francisco) and an M.A. in Old Testament theology from Berkeley's Graduate Theological Union. Her academic background has provided context for her work, particularly for the Mary Russell novels. "It's extraordinary how something completely useless like a theological degree has come in handy," King jokes.

That ability to craft a good story clearly accounts for King's popularity. "I like the demands of structure that you get in a genre novel, especially in the crime genre," she said. "It keeps the writing focused." But compelling characters, like Kate Martinelli and Mary Russell, are also important to her success. "Kate is a cop, beginning and end," King says, but her being a once-closeted lesbian in a macho and even homophobic work environment gives her an added dimension. And of course Mary Russell is a unique character, an outspoken woman who can match wits with the venerable Holmes.

King recounts how tough it was to sell the first Mary Russell novel, The Beekeeper's Apprentice. Written in 1987, the book was turned down several times before St. Martin's brought it out in 1994, thanks no doubt to her success with the first Kate Martinelli novel, A Grave Talent. "If you describe a book as a 15-year-old American girl meets Sherlock Holmes and becomes his apprentice, it sounds pretty hokey," she says. "But if you add 'and later becomes his wife,' it's decidedly kinky." That novel launched King's career, and now she has legions of fans, from teenage girls attracted by the idea of "a bright, scholarly outsider who can get the better of Sherlock Holmes," to aging Sherlockians.

Though King insists she's not the model for the indomitable Mary Russell, it's difficult not to draw parallels between the two. Both are intellectually precocious, both are interested in religion and feminism—and both are married to older men. Some years after she'd gotten her B.A., King fell in love with Noel King, one of her professors, who is now in his 80s; King herself is 53. They have two grown children, a daughter who works at the University of California at Santa Cruz in development and a son in the Army's Rangers Regiment currently serving in Baghdad.

But after two Mary Russell novels and the new Kate Martinelli book in the last three years, King says she's ready for something different: "I wanted to write a historical standalone and I wondered what would happen to a man whose experiences during the Great War had stripped him of defenses. I also wanted to write a book about the past that reverberates with the present: the 1920s phobia about a Communist takeover of Britain has much to say about our current preoccupation with another kind of terrorist." The new book, set in 1926 during London's Great Strike, is called Touchstone—"such an evocative word: tactile and unyielding, rich in alchemical and Shakespearean overtones."

King calls the book, half tongue-in-cheek, "a new genre, the country house political thriller," adding, "I'm writing the story with a lot of 'details to come' written in the margins. I need to know how a country house works, about the structure of British politics, about the whole trade union issue. But I need the story to come first."And given her track record—more than a novel a year since A Grave Talent appeared—the sales force should get ready.