The Kelvans, visitors from another galaxy, take over the Enterprise for a long voyage home.
The Enterprise is seized by the Kelvans, beings from the Andromeda galaxy who have transformed themselves into human form. They plan to take the ship home and to use the crew as part of their plans. Kirk sets out to cause trouble among the Kelvans by making them feel human emotions.
The story is notable for the way Kirk and his crew turn the invaders' new bodies against them with jealousy and appetite. Scotty has a famous drinking scene with a Kelvan. Fans enjoy the clever method of defeating a superior enemy and the unusual perspective of the aliens.