STAR TREK: #21 Tomorrow Is Yesterday, 1967

Writer: D. C. Fontana
Director: Michael O'Herlihy

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols

Captain John Christopher: Roger Perry
Computer Voice Majel Barrett
Colonel Fellini: Ed Peck
Air Police sergeant: Hal Lynch

Stardate 3113.2

The gravitational forces of a Black Star throw the U.S.S. Enterprise back in time: To the end 20th century, where they are detected by a radar over Nebraska and classified as an UFO. Captain John Christopher flies the investigating fighter plane. Unfortunately the plane is caught in the Enterprise tractor beam and destroyed. To save the pilot's life, they beam him on board. Captain Christopher is bewildred and amused by the experience, until he's told that he can't go back to Earth because, with all that he now knows, he might endanger the future. 

Later, Spock finds out that Captain John Christopher has an impact on the future of Earth and must be put back where he came from. To remove all records of the U.S.S. Enterprise sighting, Kirk and Sulu beam down to the air base, where Kirk is captured by the Air Police while Sulu brings the records on board. Spock leads a rescue party and Captain Christopher tries to take advantage of the mission to free himself, but Spock forsee his plan and manages to stop it. By accident an Air Police sergeant is beamed on board of the Enterprise and shocked by the sight of Spock, who seems to enjoy the moment. 

Spock and Scotty manage to use a slingshot effect around the Sun to make return to their own time possible. And: to bring the people back a moment before they came into contact with the Enterprise. The confused Air Police sergeant is returned without remembering anything and so is Captain Christopher, who sees the Enterprise as he saw her before- just for a tiny moment – not believing his eyes after the return. He, too, has forgotten about it. And it was him and not themselves – as Spock said – who was the first up there.