A time-travelling operative, Gary Seven, intercepts the Enterprise in 1968 and entangles it in a rocket launch.
Travelling back to 1968 to study Earth's history, the Enterprise intercepts a man named Gary Seven, who has been sent from an advanced alien species to stop a nuclear weapon being launched. Kirk wonders whether he is a threat or an ally, and Seven's assistant Roberta Lincoln and his cat Isis join the story.
The episode was a backdoor pilot for a series that was never made. It gives an interesting look at the 1960s and reminds viewers of the series' conversation about history. Fans remember it for the mysterious Isis, a cat that seems to be more than she appears.