Under the terms of the Organian Peace Treaty, Sherman's Planet will become a colony of whoever can best develop it. To that end, the Federation intends to ship a large quantity of quadrotriticale to that planet, and Federation Undersecretary Nilz Baris is determined that the grain will arrive, so he orders the manager of Space Station K-9 to issue a distress call! Enterprise responds to discover no emergency; Baris just wants guards for his grain. And then a Klingon ship arrives, seeking shore leave. And Cyrano Jones, an itinerant trader, also arrives, with some odd animals he calls tribbles. Some very hungry, odd animals...

The Horizon visited the planet Iotia a hundred years ago, long before the Prime Directive forbid interference in pre-warp alien cultures. Beaming down to investigate the damage, Kirk, Spock and McCoy discover a culture run by mobsters! It seems that Horizon left behind a book, "Chicago Mobs of the Twenties", and the highly imitative people of Iotia patterned their society after the groups described in its pages. How can Enterprise undo the grievous harm Horizon did to this civilization?