The iconic mission of the U.S.S. Enterprise comes to an end, as Kirk and his crew battle the ultimate adversary.

To solve the ultimate mystery, the Enterprise must return to where Kirk's five-year mission began. FAN NOTE: This is a follow up episode to "Where No Man Has Gone Before" (s1e03), the second pilot for the original series. This episode has characters called "espers". In the original series pilot, Mitchell said, "Man cannot survive if a race of true espers is born." FAN NOTE: The Romulan Commander character was introduced in the original series episode "The Enterprise Incident" (s3e02). The actress who played that role in the original series is the mother of the actress playing the Romulan Commander in this episode.

Kirk struggles with aiding a society whose inhabitants view their isolated world in a very unique way.

The Enterprise discovers a lost starship... with an unlikely passenger. FAN NOTE: This is a follow up episode to "The Tholian Web" (s3e09) from the original series.

While the Enterprise is sent on a seemingly routine mission, Kirk is recalled to starbase where he faces an ethical dilemma that challenges the very core of Starfleet Command.

A troubled creature pierces the Enterprise hull, pitting the crew against a pursuer that threatens to tear them apart.

Kirk and McCoy are trapped in time while an alien infestation threatens the Enterprise.

Captain Kirk finds himself haunted by guilt from his past as the fate of an alien world hangs in the balance. FAN NOTE: This episode involves original series character story lines: Rayna from "Requiem for Methuselah" (s3e19), Miramanee from "The Paradise Syndrome" (s3e03), and Edith Keeler from "The City on the Edge of Forever" (s1e28).