Stardate: 5693.2 --The Enterprise investigates the disappearance of its fellow starship the U.S.S. Defiant. Kirk takes a team over and they find the entire crew dead, having killed each other in fits of madness. 

The Defiant starts to vanish and everyone but Kirk makes it back before it disappears for good. Spock orders the Enterprise to stay in the area to attempt a recovery.But the crystalline Tholians launch an attack and the Enterprise crew start to experience the same madness that destroyed the Defiant crew.

original airdate--November 15, 1968  Remastered date-- March 31, 2007

music:Theme song  written by Alexander Courage

Goof--Chekov screams though his mouth does not move.

Trivia--This is the first time we see Lt. Uhura's quarters in the series. The other time is in "Star Trek" (1966) {Elaan of Troyius (#3.13)}, when the room was occupied by Elaan, Dolman of Elas, on the way to her wedding.

Space: the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.