The BAU is called to the San Francisco Bay area when a young couple named David Atley and Nicole Puli are found shot to death, with evidence pointing to the unsub being the Zodiac Killer, who has not been heard from since 1974. The local police detective leading the investigation believes it to be the work of the real Zodiac Killer, but Hotch, Rossi and Reid believe that it is not, especially since there has been no evolution in the nature of these latest killings since those by the real Zodiac Killer. The team nonetheless follow leads back to the original investigation, including tracking those who were involved in that investigation as well as anyone who either wrote about it or tracked the investigation. They are hindered in the investigation by an anxious and sometime media hungry public who want to cash in on the Zodiac Killer's notoriety. They are also helped and hindered when they learn the unsub has a genius IQ, he who may understand the BAU's tactics. As the BAU goes through their investigation, the unsub takes his childhood best friend on an unwanted trip down memory lane, which could be his and that best friend's downfall. Meanwhile, Reid, on meeting a fellow prodigy at a violent crimes seminar, questions whether he has achieved enough in life - which includes choosing to be an FBI agent - as he hits the milestone age of thirty.