When the U.S.S. Enterprise receives a top-priority order to protect a shipment of quadrotriticale grain on Deep Space Station K-7, Kirk is irritated to be guarding a shipment of "wheat." With Klingons taking shore leave on the space station, Federation Undersecretary for Agriculture Nilz Baris and his pesty assistant Arne Darvin inform Kirk that Starfleet Command is afraid the Klingons may try to steal the grain. Meanwhile, space trader Cyrano Jones gives Uhura a purring ball of fluff known as a tribble. Charmed by the cute creature, Uhura takes it back to the Enterprise, where it multiplies and the starship is soon overrun by the furry creatures.

William Schallert (Undersecretary Nilz Baris)
William Campbell (Captain Koloth)
Stanley Adams (Cyrano Jones)
Whit Bissell (Mr. Lurry)
James Doohan (Lt. Cmdr. Montgomery Scott)
Nichelle Nichols (Lt. Uhura)
Michael Pataki (Korax)
Edwin Reimers (Admiral Fitzpatrick)
Walter Koenig (Ensign Pavel Chekov)
Charlie Brill (Arne Darvin)
Paul Baxley (Ensign Freeman)
David L. Ross (Guard)
Guy Raymond (Bartender)

• Station K-7 is close to the Federation-Klingon border.
  
• The grain was to be grown on Sherman's Planet, also on the Federation-Klingon border, and claimed by both parties.
  
• Klingon agent Arne Darvin returned to cause even more trouble in the Star Trek: Deep Space Nine episode "Trials and Tribble-ations", which sends the DS9 crew back into this episode.