Ivar Trevelyan travels to the planet Osier, inhabited by earthling-like humanoids in the Middle Ages. In some respects, this world is more prosperous than Earth in a similar period - it is not so bloody and cruel, because the rule of law in it is supported by an all-powerful empire that has conquered the only inhabited continent of the planet. But for some reason this society does not accept the innovations of earthly progressors, and Trevelyan must find out what is the matter.