Having received a Priority One distress call from an outlying space station, the Enterprise arrives to find they have been summoned there by a Federation commissioner merely to protect a shipment of seeds meant to sow wheat on Sherman's planet. The planet is also coveted by the Klingons, who are taking shore leave at the station. The trouble arises with tribbles - small furry creatures that seem to multiply without end. However, their fortuitous presence reveals both a problem with the wheat and a traitor on the space station.