An English professor lays out a stirring hoax theory on America’s most famous cold case, launching filmmaker Andrew Nock on a journey into the world of "The Zodiac"; victims' family members talk on camera for the first time.

The hoax theory is put to the test when two computational linguistic experts study the 32 Zodiac letters; filmmaker Andrew Nock meets a witness for her first on-camera interview after years of fear that "The Zodiac" would hunt her down.