Episode Title: "ALL OUR YESTERDAYS"
Production Number: 78
Original Air Date: 03-14-69
Three and a half hours before the star Beta Niobe is calculated to go nova, the U.S.S. Enterprise scans Sarpeidon, the only Class-M planet in the system. The crew finds the planet deserted, though the planet did not have space flight capability. Captain Kirk, Commander Spock, and Dr. McCoy beam down to a library on the planet and meet the librarian, Mr. Atoz, and his android duplicates, who sent the world's population into the past before the nova, using a machine called the Atavachron. As Kirk is viewing records of a past era, he hears a woman scream and runs into a portal to investigate; he finds himself in an ancient city, where he is accused of witchcraft.
Spock and McCoy run through the portal after the captain, but find themselves trapped in the Sarpeidon ice age; there they meet a woman named Zarabeth, a prisoner of Zor Khan the tyrant, who banished her to the ice age for the actions of her kinsmen. Spock becomes more passionate, as his ancestors were 5,000 years in the past, and he consumes animal flesh. Spock falls in love with Zarabeth and wants to stay in the past, but McCoy convinces him to go back to the time portal.
Kirk finds his way back to the library and forces Mr. Atoz to help him find the period where Spock and McCoy are trapped. Once they get back through the portal, Mr. Atoz escapes into the past before the sun explodes, and the Enterprise leaves the system before the nova destroys Sarpeidon.
Factoid: Sarpeidon is the only satellite of the star Beta Niobe.
Guest Characters: *Mr. Atoz
Alien Races: *Sarpeidons
KEY: [brackets]=illusions *star=first appearance