Memory Alpha's In Universe Timeline
The Alternative Factor - Tomorrow Is Yesterday - The City on the Edge of Forever.

A Piece of the Action - Tomorrow Is Yesterday - Errand of Mercy.


the Enterprise is thrown back in time to Earth during the 1960s by the effects of a high-gravity "black star", and ends up in Earth's upper atmosphere, where it 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. The pilot, surprised to see the strange craft above him, is ordered to stop the Enterprise from escaping. Captain Kirk uses a tractor beam on the jet, which accidentally tears the plane apart. Kirk orders the pilot to be transported aboard the Enterprise to save him.

The man is at first confused by his new surroundings, then amazed by what the future holds, and impressed and awed when he discovers that Enterprise is one of 12 such starships under the authority of a combined service and that the computer calls Kirk "Dear", having been overhauled on the female-dominated planet Cygnet XIV (the technicians there thought the computer needed a personality).

Fearing Christopher could disrupt the timeline if returned to Earth after glimpsing the future, Kirk decides Christopher must stay with the Enterprise. After Science Officer Spock later discovers that the pilot's own as-yet-unborn son will play an important role in a future space mission to Saturn, Kirk realizes he must return Christopher to Earth, but without any knowledge of Enterprise or other future events.

After learning of the existence of film taken of Enterprise by Christopher's wing cameras, Kirk and Lt. Sulu beam down to the airbase to recover it. Upon obtaining the relevant computer tapes, Kirk is captured and disarmed by an Air Policeman. When Spock attempts to contact Kirk via communicator, the policeman accidentally activates an emergency signal and is immediately beamed aboard. With yet another abducted and confused native to deal with, they confine him to the transporter room.

Spock, Sulu, and Captain Christopher, knowledgeable of the base's layout, beam down to find and recover Kirk. After Kirk's guards are subdued, Christopher grabs one of their guns and demands to be left behind. Spock, out of the room, has himself transported to a position behind Christopher, where he disables him with a Vulcan nerve pinch. After they return 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. The maneuver is risky, since even a small miscalculation could destroy the ship, or make them miss their own era.

Kirk okays the maneuver, and time on board the Enterprise moves backwards. Capt. Christopher is beamed back to his fighter jet at the instant he first encountered Enterprise, preventing any evidence of the ship being produced, which somehow erases his memory of his time on the Enterprise,and the sighting is written off as just another UFO. The Air Policeman is also returned to his own time, just moments before he first stumbles upon Kirk and Sulu, and somehow his memory of his Enterprise visit is erased, too. Enterprise then successfully returns to the 23rd Century, in the right time.

Errors and ExplanationsEdit

The Nitpicker's Guide for Classic TrekkersEdit

Plot OversightsEdit

  1. Spock failing to check the history banks for records of the pilot's descendants. The immediate priority is checking for direct contributions by Christopher.
  2. Use of stardates in the log entries made while in the 20th century. The officers use stardates relative to elapsed time to ensure the log entries are placed in the correct order.

Equipment OdditiesEdit

  1. The transporter grabbing a seated individual and rematerialising him in a standing position. The transporter must have been programmed to rematerlise seated people in a standing position as a safety measure. [N 2]

Internet Movie DatabaseEdit

Character errorEdit

  1. When the bridge is first shown with many of the crew members strewn about the floor, Captain Kirk clearly looks at where Lieutenant Uhura is sprawled on the floor, yet does not make any motion to go help her until Mr. Spock notices her, and roughly lifts her into her seat.Kirk is probably too busy checking to see of the rest of the bridge crew are alright.


  1. When Kirk and Sulu first enter the Statistical Services Division office, they have to use a sonic device to unlock the door. After the sergeant is beamed back into himself on the return trip, he opens the should-now-be-locked door without a key.Perhaps something happened to prevent the lock from working.[N 3]

Factual errorsEdit

  1. Captain Christopher is assigned to Air Defense Command, and clearly shows an ADC qualification level insignia on the left sleeve of his flight suit. However, the stock footage of F-104's used on screen shows aircraft with markings from Tactical Air Command. ADC could have borrowed TAC aircraft due to a maintenance shortfall.

Incorrectly regarded as goofsEdit

  1. The Air Force Air Police are armed with Smith and Wesson Model 15 (USAF Designation M15) .38 Special revolvers that were standard issue from 1962-1992. The grips on one appear to be ivory, but are actually very worn wood This was quite common for a duty weapon.

Plot holesEdit

  1. There are security alarms for the photo lab but not the Statistical Service Section. Kirk and Sulu could have disabled these.
  2. When the ship travels back in time, the air security guard and Captain Christopher's memory is affected, but no one else's is. This could be a side effect of being transported during time travel.

Nit CentralEdit

  1. Scott McClenny on Tuesday, November 16, 1999 - 2:45 pm: Ok, now that we know about the Temporal Prime Directive from the DS9 episode Trials and Tribble-ations and the Voyager episode Relativity, now would be a good time to ask the obvious: Did Spock break the Temporal Prime Directive when he told Christopher about his son? I realize that there might not have been a TPD at that point of time..but the thing with temporal mechanics is the TPD could have come into being when they returned and they could have broken it.. as Tom Paris once said,"Is this making any sense?" Keith Alan Morgan on Tuesday, November 16, 1999 - 11:35 pm: As time travel was an accidental business at this point, there was no Temporal Prime Directive that Spock had ever sworn to uphold. Also the fact that Christopher forgot everything he had learned about the future makes it all a moot point, anyway.


  1. These are relative, based on elapsed time during the trip to the past.
  2. Listed under Continuity in the IMDB entry.
  3. Also listed under Plot Holes in the IMDB entry.

The Original Series Season 1
Pilot episodes: The Cage I Where No Man Has Gone Before
Regular episodes: The Corbomite Maneuver I Mudd's Women I The Enemy Within I The Man Trap I The Naked Time I Charlie X I Balance of Terror I What Are Little Girls Made Of? I Dagger of the Mind I Miri I The Conscience of the King I The Galileo Seven I Court Martial I The Menagerie Part 1 I The Menagerie Part 2 I Shore Leave I The Squire of Gothos I Arena I The Alternative Factor I Tomorrow Is Yesterday I The Return of the Archons I A Taste of Armageddon I Space Seed I This Side of Paradise I The Devil in the Dark I Errand of Mercy I The City on the Edge of Forever I Operation: Annihilate!