Zodiac tells the story of the hunt for a notorious serial killer known as "Zodiac" who killed in and around the San Francisco Bay Area during the late 1960s and early 1970s, leaving several victims in his wake and taunting police with letters and ciphers mailed to newspapers. The case remains one of San Francisco's most infamous unsolved crimes.
Robert Graysmith is a cartoonist who works for the San Francisco Chronicle. His quirky ways irritate Paul Avery, a reporter whose drinking gets in the way of doing his job. The two become friends thanks to a shared interest: the Zodiac killer. Graysmith steadily becomes obsessed with the case, as Avery's life spirals into drunken oblivion.
Graysmith's amateur sleuthing puts him onto the path of David Toschi, a police inspector who has thus far failed to catch his man; Sherwood Morrill, a handwriting expert; Linda del Buono, a convict who knew one of the Zodiac's victims; and others. Graysmith's job, his wife and his children all become unimportant next to the one thing that really matters: catching the Zodiac.