The U.S.S. Enterprise is appointed to transport ambassadors from many worlds to the Babel Conferences. Among those aboard are Spock's parents: Ambassador Sarek of Vulcan and his human wife, Amanda. At a cocktail party, Tellarite Ambassador Gav quarrels openly with Sarek about the admission of Coridan into the Federation. When Gav is later murdered, circumstantial evidence points to Sarek. Meanwhile, an unknown vessel is following the Enterprise.

Jane Wyatt (Amanda [Grayson])
Mark Lenard (Ambassador Sarek)
Nichelle Nichols (Lt. Uhura)
William O'Connell (Thelev)
Majel Barrett (Nurse Christine Chapel)
Walter Koenig (Ensign Pavel Chekov)
John Wheeler (Ambassador Gav)
James X. Mitchell (Lt. Josephs)
Reggie Nalder (Ambassador Shras)

• Mark Lenard previously played the Romulan commander in "Balance of Terror".
  
• This episode introduces the Andorian and the Tellarite species. Along with Humans and Vulcans, they are the two other founding members of the United Federation of Planets. The Andorians are blue-skinned with two antennae on top of their heads. The Tellarites are pink pig creatures.
  
• Spock and Sarek haven't spoken in 18 years over Spock's decision to join Starfleet instead of the Vulcan Science Academy.
  
• Vulcans show "affection" by touching their index and middle fingers to each other.
  
• Thelev was surgically altered to appear Andorian. Spock deduces that he is an Orion. The Orions wanted to block Coridan's admittance into the Federation so that they could continue to steal their dilithium and sell it for profit.