Walt Longmire, Sheriff of Absaroka County, Wyoming, has a soft spot for women who are victims of domestic violence. In the fifth entry in this popular series, his jail is housing a woman accused of violence against her husband. Mary Barstad has confessed to shooting her husband Wade in the head no less than six times. Nobody is too surprised--Wade was not popular with his neighbors, and his last act was to burn down a barn with his wife's beloved horses inside. Walt is puzzled by Mary's dreamy demeanor and her unwillingness to communicate. Though she is insistent on her guilt, something tells him she's innocent. Though the crime happened in a neighboring county, he decides to investigate, even though it means going undercover.

Dark Horse has what readers have come to expect from Craig Johnson--a vivid sense of place, wry humor, and memorable characters, including an undocumented Guatemalan barmaid who wants to be a detective--but the structure of the story is unnecessarily complex. The narrative jumps back and forth in time between Walt's undercover work and the beginning of the investigation do more to confuse than to entertain; but when finally, the story settles into a straightforward chronology, it takes off at full gallop, leading Walt into a tense duel of wits and endurance with a desperate killer. Readers who persist beyond the first half of the book will find themselves rewarded in the end.