TOS Season 2 Episode 26 Assignment: Earth

Plot

The USS Enterprise, which has time-travelled to 1968 Earth for historical research, intercepts a powerful transporter beam originating from at least one thousand light-years away. A man called Gary Seven (Robert Lansing), dressed in a 20th-century business suit and accompanied by a black cat he calls Isis, materializes on board the Enterprise. Realizing that Captain Kirk and his crew are from the future, Seven warns Kirk that history will be changed if he is not released immediately. Having no proof of Seven's claim, Kirk has him held in the brig. Meanwhile, Spock searches the history database and finds that the United States will launch an orbital nuclear weapons platform in a few hours.
Seven, with the help of his pen-sized "servo" device, escapes and beams down to an office in Manhattan, emerging from a vault door hiding a teleporter. Addressing a voice-activated computer, he identifies himself as "Supervisor 194" (code name Gary Seven) and inquires as to the whereabouts of two agents, "201" and "347", who he learns have not been heard from in three days. Seven decides to complete their mission himself. A young woman arrives, whom Seven mistakes for Agent 201, but who is actually Roberta Lincoln (Teri Garr), a secretary employed by the missing agents. Seven then tells Roberta he is a CIA agent, and, appealing to her patriotism, asks her to remain and assist him. The computer eventually discovers that Agents 201 and 347 have died in an automobile accident.
Kirk and Spock track Seven to his office. Roberta stalls them while Seven and his cat enter the vault and are teleported away. Arriving at "McKinley Rocket Base", Seven gains access to the gantry and climbs onto an access arm to begin rewiring some circuits of the soon-to-launch rocket. When Kirk and Spock pursue Seven to McKinley Rocket Base, they are immediately detained by police. On the Enterprise, Chief Engineer Scott (James Doohan) locates Seven and initiates beaming him up. At the same moment, in Seven's office, Roberta is experimenting with the vault controls and inadvertently intercepts Scotty's transporter beam, bringing Seven to the office.
Seven takes control of the rocket remotely, arming its warhead and sending it off course. McKinley Base controllers frantically try to regain control and, failing that, send a self-destruct command to the missile, without success. After a failed attempt to call the police, Roberta hits Seven with a heavy cigar box and seizes the servo. Seven pleads with her to allow him to proceed, "...or in six minutes, World War III begins!" Kirk and Spock beam to Seven's office. Seven pleads with Kirk to let him complete his plan, which is to destroy the missile at a low enough altitude to deter the use of such orbital platforms in the future. Kirk tells Spock that if he can't destroy the rocket, he will have to trust Gary Seven. Spock replies that without facts, the decision cannot be made logically. Kirk decides to trust Seven who, with only seconds to spare, safely detonates the warhead at an altitude of 104 miles.[3]
In the epilogue, Spock and Kirk explain to Seven that the Enterprise was meant to be part of the day's events, citing their historical records. Seven is curious to know more, but they reveal only that he and Roberta will have an interesting future.