Time travel shenanigans on then present-day earth! Not the strongest of the many, many, time-travel Trek episodes. Seems someone got a note that said 'lighten things up,' from the network execs: this episode goes from serious to goofy so many times I got whiplash. Majel Barrett doing a silly/sultry computer voice was fine, but I was less enthused with the accidentally kidnapped guard (Hal Lynch) mugging for the camera.
However I did get a kick out of the F-104 stock footage. Fortunately, there was no refueling.