Tomorrow Is Yesterday ()
The Enterprise collides with a black hole and is thrown back to Earth in the 20th century, where they must find a way back and erase any trace of their presence. Matters become complicated when they rescue an Air Force pilot and cannot return him without changing history...but if he disappears that will change history as well.
The USS Enterprise is thrown back in time to Earth during the 1960s by the effects of a high-gravity “black star.” Enterprise ends up in Earth’s upper atmosphere and is picked up as a UFO on military radar.
A U.S. Air Force F-104 interceptor piloted by Captain John Christopher is scrambled to identify the craft. Fearing an attack, Captain Kirk orders a tractor beam to be used on the jet, which tears the plane apart. The pilot is transported aboard the Enterprise.
Fearing Christopher could disrupt the timeline if returned to Earth, Kirk decides that the pilot must stay with the Enterprise. Spock later discovers that the pilot’s unborn son will play an essential role in a future mission to Saturn. Kirk realizes he must return Christopher to Earth after all.
After learning of the existence of film taken of the Enterprise by Christopher’s wing cameras, Kirk and Lt. Sulu beam down to the airbase to recover the film and any other evidence of their visit. They are caught by an Air Policeman, who accidentally activates an emergency signal on Kirk’s communicator and is immediately beamed aboard. Kirk and Sulu continue their search, after which Kirk is captured again, and Sulu escapes.
Spock, Sulu, and Christopher, who knows the base’s layout, beam down to recover Kirk. After Kirk’s guards are subdued, Christopher grabs one of their guns and demands to be left behind. Having anticipated Christopher would make such an attempt, Spock appears behind Christopher and disables him with a Vulcan nerve pinch.
After returning to the ship, Spock and Chief Engineer Scott inform Kirk of a possible escape method by slingshotting around the Sun to break away and return to their time. Even a tiny miscalculation could destroy the ship or send them to the wrong era.
Kirk okays the maneuver, and time on the Enterprise moves backward. Christopher is beamed back to his fighter jet before he encountered the Enterprise. Evidence of the ship is prevented from being produced and, his memory of the Enterprise is erased. The same is done with the Air Policeman. Enterprise then successfully returns to the 23rd century.