On a planet doomed to destruction, Kirk, Spock & McCoy become involved with two aliens who use them as laboratory animals in a bizarre series of tests on an alien empath who may be the savior of her planet.
Air Date: 11/22/68
Director: John Erman
One of the more bizarre episodes of the original series, believe it or not, I watched this one for the first time back in 2007. I never saw it in syndication.