In 1979, law enforcement is thrilled when the East Area Rapist (EAR) attacks abruptly stop in Northern California, but in reality, the still unknown assailant has moved south to commit a number of gruesome murders in the Santa Barbara area, known as the "Original Night Stalker" series. The hunt for the perpetrator stalls due to lack of cooperation between jurisdictions and concerns of tarnishing the area’s pristine image, leaving the community unaware of the predator in their midst. Michelle's article chronicling her investigation of the case causes a splash when it's published in 2013.

As Michelle’s loved ones cope with her sudden death, her work to unmask the Golden State Killer lives on. Inspired by McNamara’s interest in genealogy and online DNA testing services, Paul Holes, Chief of Forensics in Contra Costa County, reconstructs the killer’s family tree with the help of genetic genealogist Barbara-Rae Venter. After inheriting Michelle’s 37 boxes of case files, researcher Paul Haynes and true crime writer Billy Jensen work alongside Michelle’s husband, Patton Oswalt, to finish her book, which becomes an instant bestseller. Meanwhile, the release of Michelle’s autopsy report rocks her inner circle.