After learning that his father may have been the Zodiac killer, Gary brings The New York Times best-selling true crime author Susan Mustafa into the fold to help uncover more information about him. Over the next two years, they follow a dark trail filled with unexpected discoveries as Gary attempts to find some closure.

Gary's story takes a turn when he realizes his book could be a betrayal of his newfound relationship with his biological mother. When Gary goes up against a community of Zodiac fanatics with ulterior motives, he reveals new information that has never been shared.

Armed with DNA evidence that links his father to the Zodiac killer, Gary forges ahead trying to uncover his truth. Meanwhile, a San Francisco based private investigator digs into Susan and Gary's claims. The questions that have haunted Gary for decades culminate in an unexpected end.