"Assignment: Earth" is a second season episode of Star Trek: The Original Series. It was first broadcast on March 29, 1968 as the last original episode in the second season. It was repeated on August 9, 1968. It is episode #55, production #55, written by Art Wallace, based on a story by Wallace and Gene Roddenberry, and directed by Marc Daniels.
This episode served double duty, not only as an episode of Star Trek, but as a pilot for a proposed spin-off television series, that would have been produced by Roddenberry, under the same name, Assignment: Earth. The show would have featured actor Robert Lansing as Gary Seven, a futuristic "James Bond", as the lead character. The episode stars Teri Garr as Roberta Lincoln, who would have been a co-star in the series, had it continued on its own.
There is no stardate given in this episode.
With a gravitational slingshot around the sun, the starship USS Enterprise time travels to 1968 Earth for historical research. The ship orbits Earth using its deflector shields to avoid detection. Suddenly, the Enterprise intercepts a highly powerful transporter beam from thousands of light-years away.
A man dressed in a business suit materializes on the transporter pad. He carries a black cat with a diamond collar with one hand and a briefcase with the other. He converses with his cat, Isis, then introduces himself to Captain Kirk as Gary Seven.
Seven tells Kirk that he is an Earth human from a far more advanced world. His ancestors are humans taken from Earth over 6,000 years ago and trained to intercede on Earth to help it survive. Seven refuses to reveal his home planet and warns Kirk that history will be changed and Earth destroyed if he is not released immediately.
Kirk demands more proof, but Seven refuses. Kirk orders him taken into custody but Seven evades attempts to subdue him, even shrugging off Spock's nerve pinch. When Seven tries to beam himself down, Kirk stuns him with a phaser.
Kirk has Seven taken to the brig and asks Spock to search the history database for any critical events that will soon occur. Spock finds that the United States will launch a nuclear weapons platform from McKinley Rocket Base. The launch is scheduled in a few hours and it may be the reason for Seven's visit.
Meanwhile, Seven awakens and finds himself in a holding cell. He removes a pen -- actually an advanced "servo" weapon -- from his pocket. He disables the force field and stuns the guard. His escape is detected, but not before Seven and Isis make their way to the transporter room, stun the technicians, and beam down to New York City. Kirk and Spock follow them.
Seven enters an office and activates a sophisticated computer hidden behind a bookcase. The computer reports that agents "201" and "347" have not been heard from in three days. With only an hour until the launch, Seven decides to complete their mission.
A young woman arrives and Seven mistakes her for agent 201. He asks her to dictate a report to an electric typewriter with speech recognition. This is technology well past the state of the art in 1968 so she becomes very flustered. Seven finally asks the computer to identify her. She is Roberta Lincoln, a secretary employed by the missing agents.
Seven realizes his blunder and, appealing to her patriotism, tells Roberta he is a secret government agent and that she should remain quiet about what she has seen. Roberta had thought her employers were doing research for a new encyclopedia. An intelligent woman, she realizes something very odd is happening.
The Beta-5 computer then informs Seven that agents 201 and 347 have died in a car accident.
Kirk and Spock, dressed in contemporary clothing, follow Seven to the office. Seven has Roberta stall them while he enters his giant walk-in safe, actually the portal to a powerful transporter, and dematerializes. As Kirk opens the door with a phaser, Roberta manages to call the police. The police arrive and the two officers are inadvertently beamed to the Enterprise along with Kirk and Spock. The two confused officers are quickly beamed back down.
Seven and Isis materialize at McKinley Rocket Base. With fake IDs, Seven easily stuns a guard and stows away in the launch director's car as he makes a final check of the pad. Riding the elevator to the top of the gantry, Seven, carrying Isis, climbs an access arm to the side of the rocket, opens it and begins to rewire it.
On the Enterprise, Kirk, Spock and Scotty try to locate Seven. Meanwhile, a curious Roberta explores the office and discovers the transporter. On the Enterprise, Mr. Scott locates Seven on the rocket gantry and tries to beam him up. But Roberta, randomly operating the office transporter controls, intercepts the beam-up. Seven materializes instead in the office.
Seven is briefly furious at being beamed away before he was done. But the computer tells him he can still take manual control of the rocket after launch.
Kirk and Spock beam down to McKinley Rocket Base and are quickly captured by security guards. The missile launches.
In the office, Seven takes control of the missile, arming its warhead and targeting it to the heart of the Euro-Asian continent. McKinley Base controllers frantically try to destroy the missile without effect. Every major power on the planet goes on missile alert, ordering retaliatory strikes as soon as the missile warhead explodes on impact. Roberta, extremely perturbed by Seven's actions, tries to call the police. Seven explodes the phone line with his servo pen. He then turns back to the computer, allowing Roberta to hit him on the head and seize the servo. Roberta threatens Seven with it, excitedly telling him to stop whatever he's doing. Seven replies, "I've got to finish what I started or in six minutes, World War III begins!"
Scotty beams Kirk and Spock away from base security and sends them to Seven's office. Roberta, now totally confused, points the servo pen at Kirk. Seven manages to take it from her and hands it to Kirk, adding that it was "set to kill".
Spock tries unsuccessfully to destroy the missile with Seven's computer. Seven pleads with Kirk to let him complete his plan to destroy the missile at a safe altitude to scare the world's leaders out of their insane arms race. Kirk, perhaps mindful that Seven had just kept Roberta from killing him with his servo, decides to trust Seven. Seven retakes control of the computer and safely detonates the warhead at 104 miles altitude, only 4 miles above the safe minimum.
In the epilogue, Spock and Kirk explain to Seven that the Enterprise was meant to be part of the day's events. Meanwhile, Roberta sees that Isis has turned into a sexy woman in a leather cat suit. When she demands an explanation, Seven answers "That, Miss Lincoln, is simply my cat." When Roberta looks again, Isis is once again a cat. Seven decides to keep Roberta employed as his assistant for any future missions. Kirk and Spock beam back to the Enterprise, much to Roberta's continuing astonishment.