TOS Season 2 Episode 15 The Trouble With Tribbles

Plot

The Enterprise is summoned to Deep Space Station K7 by undersecretary Nilz Baris (William Schallert) to guard a shipment of quadrotriticale grain. Captain James Kirk is annoyed at Baris's use of a high-priority distress call for a seemingly trivial matter, and complies minimally. The Enterprise crew enjoy shore leave on the station, as does the crew of a Klingon ship under the command of Captain Koloth (William Campbell).
Interstellar trader Cyrano Jones (Stanley Adams) arrives with goods for sale, among them purring balls of fluff called tribbles. He gives one to Lt. Uhura (Nichelle Nichols), who brings it onboard the Enterprise. On both the Enterprise and the station the tribbles begin reproducing rapidly. They make soothing cooing noises and are loved by the Enterprise crew, even the stoic Spock (Leonard Nimoy). However, tribbles jump and screech in disgust when around Klingons.
On the station, a drunken Klingon insults the Enterprise, her crew, and her captain. The resulting brawl between humans and Klingons forces Kirk to cancel shore leave. Baris is terrified of possible Klingon interference with the grain project, and suspects Jones of being a Klingon agent.
Doctor Leonard McCoy and Spock are concerned that the increasing number of tribbles threatens to consume all the food aboard the Enterprise. Kirk realizes that the tribbles on the station could be a threat to the grain shipment. He is too late, however; when he opens an overhead storage compartment, he is buried chest-deep in grain-gorged tribbles. Spock and McCoy discover that many of the tribbles in the hold are dead or dying, suggesting the grain has been poisoned.
Infuriated, Baris vows to see Kirk punished for the fiasco, while an equally outraged Koloth demands an apology from Kirk for what he considers disrespectful treatment of his crew. Their arguments are cut short, however, when Baris's assistant Arne Darvin (Charlie Brill) walks into the room and the tribbles react as if in the presence of a Klingon. McCoy reveals Darvin to be a Klingon disguised as a human; Darvin confesses to having poisoned the grain.
Jones is ordered to remove the tribbles from the station (a task that Spock estimates will take 17.9 years), or he may face charges for transporting dangerous life forms. Just before the Klingons depart, all the tribbles aboard the Enterprise are transported onto the Klingon vessel by Chief Engineer Scott (James Doohan), where, in his words, "they'll be no tribble at all."