The Man Trap
Kirk and McCoy beam down to a remote settlement where two scientists have been working to give them routine medical exams. One of the scientists, an old flame of McCoy's was actually an alien in disguise, and gets lose on the Enterprise, killing crewmen, until she is discovered and stopped.
- Nancy Crater: Jeanne Bal
- the monster: Francine Pyne
- Professor Robert Crater: Alfred Ryder
- Crewman Darnell: Michael Zaslow
- Crewman Green: Bruce Watson
- Uhura's Crewman: Vince Howard
Charlie Evans, a 17 year old boy orphaned at 3 on an alien planet, was rescued by the U.S.S. Antares and transfered over to the Enterprise. Charlie had been given powers by the Thasians that raised him to help his survive. However, he has no clue how to deal with other human beings, nor how to exercise self-control over his powers. He wrecks havoc on the Enterprise, until the Thasians come and take him back to Thasus.
- Charlie Evans: Robert Walker, Jr.
- Thasian: Abraham Sofaer
- Yeoman Tina Lawton: Patricia McNulty
- Captain Ramart: Charles J. Steewart
- Tom Nellis: Dallas Mitchell
Where No Man Has Gone Before
The Enterprise encounters a force field at the edge of the galaxy. The aborted attempt to cross through it leave several crewmen dead, and one with extraordinary powers. Kirk must face the unpleasant task of abandoning this crewman, Gary Mitchell, who his also his best friend.
- Lt. Comm. Gary Mitchell: Gary Lockwood
- Dr. Elisabeth Dehner: Sally Kellerman
- Lt. Lee Kelso: Paul Carr
- Dr. Piper: Paul Fix
- Lt. Alden: Lloyd Haynes
The Naked Time
A crewman, Joe Tormolen, picks up a disease on a frozen planet. The disease, which also killed the people on the planet, spreads quickly among the crew. The disease relaxes inhibitions, and brings out the person's true nature. McCoy eventually finds an antidote, but in the mean time, Lt. Riley takes over engineering and shuts down the engines. With the Enterprise spiraling down in orbit, Kirk, Spock and Scotty have to use an unorthodox method to restart the engines and save the ship.
- Lt. Kevin Riley: Bruce Hyde
- Joe Tormolen: Stewart Moss