When one member of the Pyris VII landing party returns to the ship dead, Kirk, Spock and McCoy beam down to find a house of horrors, and Scotty and Sulu transformed into mindless zombies. Two beings known as Sylvia and Korob appear as witch and warlock, sent on a mission of conquest.

Antoinette Bower (Sylvia)
Theo Marcuse (Korob)
James Doohan (Lt. Cmdr. Montgomery Scott)
George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Walter Koenig (Ensign Pavel Chekov)
Mike Barrier (Lt. Vincent DeSalle)
John Winston (Lt. Kyle)
Rhodie Cogan (First Witch)
Gail Bonney (Second Witch)
Maryesther Denver (Third Witch)
Jimmy Jones (Crewman Jackson)

• DeSalle is now the Assistant Chief Engineer. Kirk puts him in charge of the Enterprise while they are on the surface.
  
• Thankfully, this is the only Halloween episode produced for any Star Trek series.
  
• James Doohan lost his right middle finger during WWII. Most of his scenes are shot to hide it, however, it is very noticeable in this episode.