It is a straight historical and mystery story, set in the Byzantine Empire during the reign of Constantine V. In the village of Abrostola, a prosperous farmer named Theodore is murdered. As he'd alienated a few people in the village, there is no shortage of suspects. However, the village is hesitant to go the authorities in nearby Amorion. Constantine V's reign is ferociously iconoclastic, but Abrostola has escaped the government's notice. The village wants to keep its icons, but doesn't want a murderer to go free. So the village priest Father George is given the task of finding the killer.
The introduction to the story found in Crime Through Time III states that "Farmers' Law" is Turtledove's first mystery story. However, both "Les Mortes d'Arthur" and "The Maltese Elephant" were mystery stories published earlier. On the other hand, the former story is a mystery in a science fiction setting, and the latter is a pastiche-spoof of a 1920s novel. "Farmers' Law" is absent of both fantastic elements and parody.