Faye Kellerman, Jonathan Kellerman, . . Warner, $23.95 (304pp) ISBN 978-0-446-53296-9

Those who admire risk, take note: two authors at the top of their game have done something quite new. Those who fear change, take heart: the results are just fine. Faye and Jonathan Kellerman, each with a slew of bestsellers, have collaborated on a volume comprising two mystery novellas. Each stands on its own, with separate settings (Santa Fe and Boston) and separate pairs of homicide detectives. To further heighten the distinction, the book has two front covers, with the authors alternating first billing and a "flip" format. It's intriguing to imagine how these two pros went about writing together, but it's even more fun just to jump in and enjoy. The characters are all new, and so are the locales; that in itself is worthy of admiration. Surprisingly, the two novellas are uneven in quality. The Boston piece, about the mysterious death of a young basketball star, suffers from wordiness and a somewhat murky plot, troubles that short works can ill afford. But the strong Santa Fe story more than compensates, with its fully rounded characters and evocative sense of place. The final scene, haunting and heartbreaking, shows the assured hand of a master. (One-day laydown Oct. 5)

Forecast: With a 300,000-copy first printing and the unusual husband-wife pairing, expect plenty of media attention and a run on bestseller lists.