14. All Our Yesterdays
If the world ended tomorrow, where would you go? What would you do? Would you spend it with your family? Would you do the things you never dreamed of doing? Or would you use a portal to travel back in time long before the oncoming storm? On the planet Sarpeidon, where their star is to go nova within hours, the inhabitants retreated into the planet's past through a "City on the Edge of Forever"-esque doorway through time. When Kirk hears a distant scream on the planet surface, he accidentally ends up in a period similar to 17th century Earth on the planet; when Spock and Bones give chase, they accidentally overshoot Kirk by several thousand years and emerge in Sarpeidon's last ice age. Kirk ends up in jail for aiding and abetting a thief, while Spock and Bones encounter a woman named Zarabeth, another Sarpeidon refugee, with whom Spock falls in love. Spock begins to exhibit primitive Vulcan impulses of violence and instability as a result from living in a time when Vulcans were barbarians, while Kirk is suspected of being a witch for being able to talk to Bones and Spock through the time portal. Upon discovering that their physiological structure was altered during time travel and that the portal only goes safely one way, they must discover a way to return to their own time alive.
13. The Enemy Within
A transporter malfunction causes Captain Kirk to be split into two separate manifestations: one weak and incapable of giving commands, the other vicious and prone to violence, an "evil" Kirk. The "evil" Kirk assaults Yeoman Rand, accosts Dr. McCoy and incapacitates several crew members. After the "evil" Kirk tries to take command of the ship and leave the rest of Kirk's away team to freeze to death, Spock transports both Kirks directly from the bridge into the transporter room as one Kirk, just the way it should be.