Timothy Wurnel is a scientist trying to perfect a gamma ray device which will place humans into suspended animation. He tests it out on a cat.
Satisfied, Wurnel turns the machine on himself, hoping to awaken in an era which will be free from war and death. He sets the machine to make him lie in suspended animation for 1,000 years. When he awakens, he finds that the Earth is indeed a utopia - but there are no humans. The Earth has been overrun by Cat People!
These civilized Cat Men (check out the suits) thought they had purged the Earth "of all the living but cats!" Whoa, even cattle or anteaters? What'd they ever do to you Cat People? Anyway, a Cat Man announces "By the power invested in me by the Cat Kingdom, I sentence you to death!" They have to take Wurnel to a museum to find an execution device and on the way they point out another exhibit.
You maniacs! You finally did it!
The surprise twist of this story is obviously that we should abandon the use of animals in the laboratory, lest they rise up and overthrow us. Free the lab cats now!