In Grass Town, Dean Smith is a very rich breeder who has lost his mind and has unlimited admiration for Napoleon I. He decides to become the emperor of the United States. Under the influence of a venal desperado, Buck Ritchie, aided by a pleutre population and by antipathy for General Grant "the usurper", he makes Grass Town the capital of the United States. It is in this wretched context that Lucky Luke intends to give back to all these protagonists