Sixties City: Assignment: Earth

Gary Seven
Robert Landing

Roberta Lincoln
Teri Garr

Cromwell
Don Keefer

Colonel Nesvig
Morgan Jones

Sergeant Lipton
Lincoln Demyan

Isis the Cat Woman
Barbara Babcock

Voice of Mission Control
Bartell LaRue

Cape Kennedy radio voice
James Doohan

Using the gravitational slingshot effect the Enterprise has travelled back in time to 20th century Earth on a historical research mission. While assuming a high orbit around the planet the ship accidentally intercepts an immensely powerful transporter beam that apparently originates over one thousand light years away. What appears to be a human male in a contemporary business suit and carrying a black cat materialises on the Enterprise transporter pad. He appears to converse with the cat, called Isis, before addressing Kirk and introducing himself as Gary Seven.

He tells Kirk that he is a 20th century human and has been living on a planet far more advanced in technology than Earth as one of a group of agents, dedicated to protecting Earth, that are descended from people taken from the planet six thousand years ago. Gary Seven refuses to reveal the location and name of the planet to a disbelieving Kirk but warns him that history will be changed and that Earth will be destroyed in the near future if he is not released immediately. Kirk insists on some proof and tries to have him arrested but the man resists them, even proving to be immune to Spock's Vulcan neck pinch. As he tries to beam himself down to the planet Kirk stuns him with a phaser.

Spock checks the computer's history banks and finds that the launch of a nuclear weapons platform by the United States is due to take place that day and must be the critical factor. Gary Seven escapes from the ship's brig with the help of his 'servo-pen' that he uses to immobilise his guard and neutralise the cell's containment field. Despite setting off security alarms he and Isis manage to make their way back to the transporter room and beam down to their destination, leaving Kirk and Spock with little choice but to follow them. In an office on Earth a computer informs Gary Seven that the two agents, '201' and '347', assigned to prevent the launch of the platform have been out of contact for three days and have not carried out their mission.

With only an hour to go until the launch Gary Seven makes the decision to carry out the mission himself. A pretty girl arrives at the office and is mistakenly believed by Gary to be one of the missing agents. He has already given her enough information to make her curious about him before the computer identifies her as the agents' secretary, Roberta Lincoln. She has been unaware of the identity or the occupations of her employers and Gary Seven persuades her that he is working for the government. As Kirk and Spock arrive on the surface and locate the office, Gary Seven discovers that his two agents have been killed in a car crash.

While Roberta delays Kirk and Spock in the outer office he uses a concealed transporter to beam to the launch site and manages to get on to the launch platform itself where he opens a panel and starts to rewire the circuitry. Back in the office Roberta has been nosing around and starts fiddling with the controls of the transporter. On board the Enterprise Scotty has managed to locate Gary Seven and attempts to transport him up to the ship. As the beam is activated Roberta presses a button in the office and Seven is taken back there instead of to the Enterprise. The computer advises him that he can still take control of the rocket even though he had not completely finished his work. As he sends a command to arm the platform Roberta phones the police. Seven disables the phone with his servo-pen which Roberta grabs and refuses to return, despite him trying to convince her that the armed device is now heading back towards Earth.

Scotty uses the transporter to rescue Kirk and Spock, who have been arrested by security at the launch site, and sends them to Seven's office where they retrieve the servo-pen from Roberta and allow him to use his futuristic devices to detonate the warhead while it is still at a safe height. This turns out to be the correct decision, which Spock confirms by accessing the history databanks. While the three men discuss the events Roberta glances at Isis who appears to her in the form of a gorgeous, black-clad human female. If , now knowing of his existence, Roberta agrees to continue working with Gary Seven, life is likely to become quite interesting in the future.