The Menagerie is the only two-parter in the original Star Trek series. It uses footage from the show's pilot, "The Cage," which had a different cast except for Leonard Nimoy as Spock, and Gene Roddenberry's wife-to-be, Majel Barrett, who played the First Officer in the pilot and Nurse Chapel in the rest of the series.
In "The Cage," which did not air until 1988, the crew of the Enterprise, led by Captain Christopher Pike, responds to a distress signal from a planet. When they arrive, they find members of a scientific expedition that had crashed on the planet 18 years earlier, including a beautiful woman named Vina.
Yet all is not what it seems. Pike is captured by a race of big-brained subterranean humanoids, and he learns that the crash survivors, except Vina, were illusions created by the aliens. Vina, was badly disfigured in the crash, but she is able to maintain an appearance of health and beauty with the help of the creatures.
"The Menagerie" constructs a frame around "The Cage," with Spock on trial for court martial after he attempts to bring his former commander, who himself has since been paralyzed, to the planet. The episode was actually an attempt by the producers to catch up on production by constructing a two-part episode in a single week using previously unaired footage. It is one of two Star Trek episodes to win a Hugo Award.