Guest stars:

Charles Drake           Commodore Stocker
Sarah Marshall          Dr.Janet Wallace, expert in endocrinology and old love of Kirk's. She appearantly was going to marry Kirk but they "called it off".

Beverly Washburn        Lt. Arlene Galway, member of landing party who dies of old age after exposure to the disease

Felix Locker            Robert Johnson, scientist on Gamma Hydra 4, dies of old age

Carolyn Nelson          Yeoman Atkins
Laura Wood              Mrs. Elaine Johnson, scientist on Gamma Hydra 4, who dies of old age.

Alvin, dead scientist that scares Chekov and protects him from getting the aging disease by a surge of adrenalin

Crew Appearances:
Landing party-Kirk, Spock, McCoy, Chekov, Scotty
On ship-Nurse Chapel
Sulu
Uhura

Stsory:

On a routine mission to Gamma Hydra IV experimental station, Kirk and a landing party are exposed to a fatal disease which causes accelerated aging. All of the landing party but Chekov are affected.  With the leadership of the Enterprise now in the hands of arthritic, grumpy old men, passenger Commodore Stocker, who is going to a new assingment at Star Base 10, assumes command. Due to inexperience, he takes the wrong course, violating the Romulan Neutral Zone. Of course, the Enterprise comes  under attack. McCoy  comes up with  a formula to combat the disease.

Gamma Hydra 4- a class M planet (O2/N2 atmosphere) situated close to the Federation/Romulan Empire neutral zone, is home to an experimental station which passes through a comets tail that carries a disease that causes rapid aging in humans.

Corbomite device: used as a  bluff to help the Enterprise escape attack by the Romulins, who are not shown in person, but only their "bird of prey" ship.

Quotes"
"Give us some more blood, Chekov. The needle won't hurt, Chekov. Take off your shirt, Chekov. Roll over, Chekov. Breath deeply, Chekov, Blood sample, Chekov. Marrow sample, Chekov, skin sample, Chekov. If I live long enough, I'm going to run out of samples." a disgusted Chekov.
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"I'm not a magician Spock just an old country doctor" McCoy.
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"She's dead." McCoy.
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"How long do you think we have?"
"Well, a matter of days, perhaps hours." This has become a very "Trek" phrase used in several episodes and movies.
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