After Spock contracts a fatal illness, the Enterprise attempts to rendezvous with the S.S. Huron, which carries the cure, but the Huron has been raided by Orion pirates.

William Shatner (Captain James T. Kirk)
Leonard Nimoy (Commander Spock)
DeForest Kelley (Dr. Leonard H. McCoy)

George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Majel Barrett (Nurse Christine Chapel)
James Doohan (Lt. Cmdr. Montgomery Scott)

• With Spock out of commission, Lt. Arex takes over the science bridge station.
  
• The characters refer to the ship as the S.S. Huron, though the ship is shown on-screen as the U.S.S. Huron NCC-F1913.
  
• James Doohan also voices Huron's Captain O'Shea and the Orion captain.
  
• The "Orion" species is pronounced with the first syllable accented as "ORE-eeon" in this episode. And instead of green skin, they have pale blue skin.