Raised from boyhood by non-corporeal beings, 17 year old Charles Evans is picked up and transferred to the Enterprise. On board the ship, the teenager proves dangerously unable to wield his enormous psionic powers with maturity.

Rescuing the crew of a ship from an asteroid belt, the Enterprise plays host to conman extraordinaire, the cunning Harry Mudd and his cargo: three beautiful women looking for suitors.

Helping nurse Christine Chapel search for her fiancé the enterprise finds a detached Dr. Kirby working on a plan to create Android duplicates of key figures, beginning with James Kirk.

Threatened by the sinister captain of a powerful alien vessel, Kirk claims that the Enterprise carries a powerful explosive which will destroy both ships. The move produces unexpected actions from the alien adversary.

Despite the earlier Romulan war, the Romulans have never been seen in person. The Enterprise, in pursuit of a Romulan aggressor, makes a discovery that causes suspicion about a senior crew member.

The crew of the Enterprise are held captive by an alien who turns out to be the Greek god Apollo.

The crew of the USS Enterprise deals with an indestructible planet-destroying space probe.

A transporter mishap swaps Captain Kirk and his companions with their evil counterparts in a parallel universe. In the so-called Mirror Universe, the Enterprise is a ship of the Terran Empire, an organization as evil as the United Federation of Planets is benevolent.