In a police procedural, the writer faces an intriguing paradox: how to present the authenticity of a criminal investigation while mystifying readers enough that they'll keep turning pages. Finding this balance can be tricky to achieve, but when the procedural is No. 20 in a hugely successful series, finding that balance must be even more difficult. Because as readers of a procedural series, we expect that the investigation will respect our intimacy with the characters, our accumulated knowledge of the settings and our demands for a fresh engaging plot.

In "Storm Prey" (Putnam, 408 pages, $27.95), John Sandford's latest featuring Lucas Davenport and his band of smart, sexy urban cowboys (yes, Virgil's in town, too), Sandford juggles all of the above as creatively as he ever has without sacrificing his characteristic staccato style.

One of the ways he successfully achieves this aesthetic balance is that in "Storm Prey" he weaves two plots with life-and-death implications, and each plot deepens our relationship with the characters we've come to love. Lucas' wife, Weather Karkinnen, is a surgeon working with a team at the Minnesota Medical Center to separate conjoined twins. Arriving at the center early one morning to begin the twins' surgery, she swerves to avoid a van fleeing the scene of a robbery in the hospital's pharmacy. The robbers have left behind a dying man and empty shelves. The crime sends ripples of violence across the Twin Cities and into Wisconsin as Davenport and his crew scramble to identify and then to catch the robbers before they eliminate Weather, their only witness.

As Davenport's investigation unfolds, so does the drama in the operating room. Weather and her surgical team struggle to defy the odds that one or both of the babies might not survive the operation. Like a good journalist and a master storyteller, Sandford makes the anatomy and the intricate procedure of the twins' surgery as suspenseful and as compelling as the criminal investigation occurring around it.

In fact, the parallels Sandford creates between the procedure to separate the twins and the hunt to sever the evil that's spilled out as a result of the robbery heighten the tension in the story and add a rich moral dimension to "Storm Prey."

Carole E. Barrowman teaches at Alverno College in Milwaukee and blogs at