Merciless

FBI special agent Mercy Gunderson gets her sternest test yet as her high-octane third adventure (after 2011’s Mercy Kill) finds the former Army sniper still adjusting to her new job, her romantic relationship with Sheriff Mason Dawson, and the one-quarter Minneconjou Sioux blood that makes her technically but not truly part of the tribe. Escaping the boredom of training sessions in Rapid City, S.Dak., Mercy begins her first murder case after 17-year-old Arlette Shooting Star, the niece of the Eagle River Reservation’s tribal president, is found stripped and staked through the heart. Mercy’s questioning of her superiors soon relegates her to doing research in the tribal archives, but this menial task leads her to uncover a string of possibly related deaths, setting the stage for a confrontation with a ruthless psychopath. Shamus-winner Armstrong continues to flesh out her singularly strong if conflicted heroine in this satisfying series entry. Agent: Scott Miller, Trident Media Group. (Jan.)