Delving into the world of online chat rooms and crime blogs, writer Michelle McNamara becomes immersed in the graphic details of the Golden State Killer case, connecting with like-minded sleuths, trading facts, photos and leads. After pitching a story to Los Angeles Magazine, she hits the ground running, interviewing several EAR survivors and retired detectives who worked the case.

Michelle McNamara reflects on the 1984 murder of her childhood neighbor Kathy Lombardo, which she credits with planting the seed for her lifelong fascination with unsolved crimes. Local detectives who worked the East Area Rapist (EAR) case in the ‘70s – and citizen detectives who picked up where they left off – discuss a proliferation of serial rape cases in Northern California at the time, discussing an era when victims were often too ashamed to speak out and sexual crime was minimized in the press and the courtroom.

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.

Michelle and her editors agree to push her book deadline after being granted access to the Orange County Sheriff’s Department’s East Area Rapist / Original Night Stalker (EAR/ONS) room. Poring over 37 boxes of files now occupying her daughter’s playroom, Michelle and her researcher Paul Haynes explore the case of the “Visalia Ransacker,” the perpetrator of a string of burglaries in the early ‘70s bearing striking similarities to EAR.

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.

As 72-year-old former police officer Joe DeAngelo’s arrest unfolds in real time, chilling facts materialize that illuminate Michelle’s prescience in her book’s epilogue, “Letter to an Old Man.” Researcher Paul Haynes and true crime writer Billy Jensen try to learn everything they can about DeAngelo. When Patton Oswalt, Jensen, and Haynes connect with survivors and McNamara’s fellow citizen detective Melanie Barbeau, Michelle’s absence is deeply felt. Series finale.