Sal and Ken investigate San Francisco, the epicenter of the Zodiac Killer murders, as the Code Team announces extraordinary news: A team member has solved the Zodiac's infamous Z340 code, which has eluded codebreakers for 50 years.
The FBI releases secret files on the mysterious Zodiac Killer, and a handwriting analyst connects the Zodiac's letters to a taunting letter mailed 3,000 miles away in Albany, NY.
The hunt uncovers a bizarre new cipher related to the Zodiac Killer, while the team's supercomputer uncovers a weird lunar pattern linking the killings. A second prime suspect emerges.
The hunt uncovers clues that the Zodiac Killer may have served in the U.S. Armed Forces, as the team's supercomputer identifies symbols in the killer's code that only a few would know.