• Production Code: 66
• Stardate: not given
• Original Air Date: Nov 1, 1968
• Writer: Jerome Bixby
• Director: Marvin Chomsky
• Guest Stars:
  • Michael Ansara (Kang)
  • Susan Howard (Mara)
  • David Ross (Lt. Johnson)
  • Mark Tobin (Klingon)

Having both received distress calls from a besieged planet, the Enterprise and a Klingon ship arrive simultaneously, and Kang, the Klingon captain, forces Kirk to beam a party of Klingons aboard the Enterprise. The ship then runs into an area of turbulence, and automatic emergency systems close bulkheads on most of the ship. The Klingons escape into the Enterprise to battle an equal number of the ship's crew. Both Klingons and Federation officers blame the ship's problems on each other, and some individuals even see the opportunity to settle scores with their arch-enemies, but nobody realizes the real catalyst behind the violence.

Note: Michael Ansara reprises the role of Kang in a visit to Deep Space Nine in the 1994 episode "Blood Oath."