Guest stars:

Jane Wyatt              Amanda, Spock's mother, human
Mark Lenard             Vulcan Ambassodor Sarek, Spock's father (also played the Romulan Commander in Balance of Terror)
William O'Connell       Thelev, an Orion surgically altered to look like an Andorian, placed in the andorian ambassodor's party to spy and sabotage the conference.

Reggie Nalder           Sharas (?)
John Wheeler            Gav, Tellerite ambassodor
James X. Mitchell       Lt.Josephs, security officer who finds Gav murdered.
 

Crew appearances:
Kirk, Spock, McCoy
Uhura
Chekov
Nurse Chapel
 

The Enterprise is  full of interplanetary diplomats en-route to a conference on Babel. Among them are Spock's father, Sarek, to whom Spock hasn't spoken in years, and his mother, Amanda. When a Tellarite is murdered, Sarek is the prime suspect but before the truth can be learned, Sarek suffers a heart attack. His only hope is a transfusion from Spock, who has replaced a wounded Kirk and refuses to leave the bridge.

Corridon-planet with a wealth of dilithium crystals subject of the conference being held on Babel whether to admit it to the federation or not.

Babel. a planetoid code name.

Talshiya- a vulcan method of humane execution, breaking the neck

Quotes:
"He's dead Jim." may have been spoken but my tape was cut here.
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"Well, I'm glad somebody's asking me something around here."
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"Well, what do you know, I finally got the last word."