In October 2014 the body of Sofia Molina is found near the train tracks toward the north end of Healdsburg. The next morning Mary, a retired physician, finds her neighbor, Mabel Garrity, strangled to death. Detective Greg Davidson leads the investigation of both murders.

Greg and his team discover that Sofia was having a series of sexual encounters with various married men. They also learn that Mabel was a gossip and a blackmailer. This knowledge results in multiple potential suspects, including Frank James, who had sex with Sofia the night she was murdered and who lives across the street from Mabel.

In the meantime, Greg hasn't seen his younger sister for forty years. He believes himself responsible for a traumatic injury she suffered when she was six years old. Now she wants to meet, filling him with anxiety.

Greg, who's already in a relationship, finds himself emotionally drawn to Mabel's neighbor, Mary. He recognizes the murderer's voice when he tries to call Mary and realizes she's in danger.