Kirk and his crew are at deadly risk from an alien creature that feeds on the salt in a human body and can take on any form.

Charlie Evans, the sole survivor of a transport crash, is transferred to the Enterprise from a different ship. Why are they so eager to rid themselves of him, though? There's more to Charlie than meets the eye...

While exploring the edge of the galaxy, the Enterprise encounters an energy barrier that gives some crewmen strange powers.

A strange alien substance causes the crew to lose their inhibitions.

A transporter malfunction causes Captain Kirk to split into his "good" and "evil" selves, and a landing party will freeze to death if they don't merge the two back together.

The Enterprise picks up a intergalactic conman, Harry Mudd, and three incredibly beautiful women who harbor a dark secret.

Nurse Christine Chapel is reunited with her old fiance on Exo III, but the scientist has plans for Captain Kirk and the Federation.

Kirk and a landing party are stranded on a planet due to a disease that causes any adult to die a painful death, and must deal with the local children who have survived.

Kirk investigates an experimental facility for holding prisoners and finds a sinister scheme.

The Enterprise encounters a vast alien ship that threatens the Enterprise with destruction.

Spock kidnaps his former captain, the crippled Christopher Pike, and heads for a quarantined planet, putting his career and Kirk's life on the line.

Spock's court-martial continues as he attempts to justify his abduction of Pike, the theft of the Enterprise, and his heading for a planet declared forbidden by Starfleet.

Kirk is one of the last survivors who can identify a mass killer, who lurks among a Shakespearean troupe aboard the Enterprise.