The Grim Sleeper follows LA Weekly reporter Christine Pelisek (Walker) as she doggedly investigates the unsolved murders of dozens of women in Los Angeles and soon realizes one person is responsible for many of these deaths that began over 20 years earlier. After a string of murders in the 1980s, the violence seemed to end; but almost 14 years later, another murder spree begins, leading Pelisek to dub the killer "The Grim Sleeper." The reporter-turned-amateur detective notices similarities between the cases and sets out to break the story of her career, researching evidence and interviewing witnesses for clues to the killer's identity. While police and lead detectives (Hudson, O'Neill) kept the community in the dark about a potential serial killer on the loose, Pelisek contacts the victims' families to offer them the truth about what may have happened to their daughters, sisters, wives and mothers. When the only known survivor (Gray) comes forward to tell her side of the story, pieces of the mystery unravel and Pelisek is even more determined to bring justice for the victims.