Lucky Luke and Jolly Jumper arrive in Grass Town and make the acquaintance of Smith I, Emperor of the United States! A local rancher gone a bit looney, he's given his cowboys fancy uniforms and replaced their Colts with sabres, and he believes he's the true ruler of the country. The citizens of Grass Town publish his harmless proclamations in the newspaper. But is he truly harmless? What will Luke do if something upsets the relationship between the Emperor and his not-so-loyal subjects?