Chapel, and made her first of many recurring appearances in "The Naked Time". Grace Lee Whitney appeared in eight episodes as yeoman Janice Rand, beginning with "The Man Trap". Whitney left the series after "The Conscience of the King", but would later make minor appearances in the first, third, fourth, and sixth Star Trek films as well as one episode of the companion series Star Trek: Voyager. Star Treks first season comprised 29 episodes, including the two-part episode "The Menagerie", which includes almost all of the footage from the original pilot, "The Cage". Other notable episodes include "Balance of Terror", which introduces the Romulans; "Space Seed", which introduces Khan Noonien Singh and serves as the basis for Star Trek II: The Wrath of Khan; "Errand of Mercy", in which the Klingons make their first appearance; and the critically acclaimed, Hugo-Award-winning episode "The City on the Edge of Forever", which features Kirk, Spock, and McCoy traveling into the past through the Guardian of Forever. Season 2 (1967–68) The show's 26-episode second season began in September 1967 with "Amok Time", which introduced actor Walter Koenig as Russian navigator Pavel Chekov, and granted viewers the first glimpse of Spock's homeworld, Vulcan. The season also includes such notable episodes as "Mirror, Mirror", which introduces the evil "mirror universe"; "Journey to Babel", featuring the introduction of Spock's parents Sarek and Amanda; and the light-hearted "The Trouble with Tribbles", which would later be revisited in a 1973 episode of Star Trek: The Animated Series and a 1996 episode of Star Trek: Deep Space Nine. The season ended with "Assignment: Earth", an attempt to launch a spin-off television series set in the 1960s. Season 3 (1968–69) After Star Treks second season, NBC was prepared to cancel the show due to low ratings. Led by fans Bjo and John Trimble, Trek viewers inundated NBC with letters protesting the show's demise and pleading with the network to renew the series for another year. After NBC agreed to produce a third season, the network promised Gene Roddenberry that the show would air in a favorable timeslot (Mondays at 7:30 p.m.), but later changed the schedule so that Trek would air in the so-called "death slot"—Friday nights at 10:00 p.m. In addition to the "mismanaged" schedule, the show's budget was "seriously slashed" and Nichelle Nichols described the series' eventual cancellation as "a self-fulfilling prophecy". Star Treks final, 24-episode season began in