A new hunt for the mysterious Zodiac Killer gains unprecedented access to files, unearthing a complicated cypher that may contain the killer’s name, and links between the Zodiac Killer and an unsolved case. A prime suspect with code training emerges.

The hunt uncovers clues that the Zodiac Killer may have served in the U.S. Armed Forces, as the team’s supercomputer identifies strange symbols in the killer’s code that would have been known to only a few when it was written. Sal and Ken find new evidence that may lead to the killer.

The hunt uncovers a mysterious new cipher related to the Zodiac Killer, while the team’s supercomputer uncovers a strange lunar pattern linking the killings. A taunting riddle by the killer may lead to a body. A second prime suspect emerges.

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.