"That Which Survives" is the seventeenth episode of the third season of the American science fiction television series Star Trek.
Written by John Meredyth Lucas (based on a story by D.C. Fontana under the pseudonym Michael Richards) and directed by Herb Wallerstein, it was first broadcast January 24, 1969.
The ship begins to accelerate uncontrollably, and Scott discovers the emergency overload bypass has been sabotaged.
Strong power emanations lead the landing party to a hidden entrance in a rock face.
McCoy surmises that the disease eventually wiped out the entire Kalandan species, and Spock suggests that the computer used images of Losira to do the job of defense.
Kirk concludes that the landing party survived because the reproductions were so perfect that they experienced regret about killing.
[1] This is the second appearance of Naomi Pollack on Star Trek, this time as Lieutenant Rahda, taking Sulu's place at the helm.
Booker Bradshaw as Dr. M'Benga previously appeared in the Season 2 episode "A Private Little War".
He found the stranding of the landing party a refreshing predicament for the series, and praised the depiction of both Spock's strengths and weaknesses as a commander, but questioned why the planet's defense system was so needlessly aggressive, and called the ending an unsatisfying info-dump.
[2] This episode was released in Japan on December 21, 1993 as part of the complete season 3 LaserDisc set, Star Trek: Original Series log.3.