Ep 23. All Our Yesterdays

Captain Kirk and his crew journey to the planet Sarpeidon, which is on the verge of destruction due to its sun going nova. However, upon arrival, they find that the planet is already deserted, except for a library containing all of the planet's history and culture. They are then surprised to find a scientist named Mr. Atoz, who seems to be the only inhabitant left on the planet. Mr. Atoz leads them to a special portal that allows them to travel back in time and witness different periods of Sarpeidon's history.

As Spock, McCoy, and Kirk are exploring Sarpeidon in different eras, they become separated from each other. Spock finds himself in a time period where the planet's inhabitants were just learning how to use fire, while McCoy finds himself in a time when the planet was highly advanced and about to be destroyed. Meanwhile, Kirk ends up in a time period where Sarpeidon is facing destruction and the inhabitants are preparing to leave the planet.

As each member of the crew travels through different periods of time, they encounter various challenges and experiences that test their knowledge and adaptability. Eventually, they realize that in order to return to their own time, they must find a way to retrieve each other from their respective time periods.

Overall, the episode explores the idea of time travel and the effects it can have on an individual's perception of reality. It also delves into the nature of change and how it can be both positive and negative, depending on the circumstances. Additionally, it highlights the importance of preserving history and culture, as well as recognizing the value of diversity in society.