When detective Libby Tate returns to the lawless New Mexico town where her father and brother were murdered, she has a single clue—an S carved into the earth. And a single suspect—Reies Coulter. She soon learns that no one in Sidewinder can be trusted, least of all the mysterious rancher. After meeting this human sidewinder in the flesh, Libby is targeted by someone who wants her dead and is torn between her suspicions and desire.