The story, which is told in the first person, centers on down-and-out actor Lawrence Smith (stage name Lorenzo Smythe, also known as “The Great Lorenzo”). A brilliant actor and mimic, he is down to his last coin when a spaceman hires him to double for an unspecified public figure. It is only when he is on his way to Mars that he finds out he will have to impersonate one of the most prominent politicians in the solar system (and one with whose views Smith deeply disagrees): John Joseph Bonforte. Bonforte is the leader of the Expansionist coalition, currently out of office but with a good chance of changing that at the next general election. Bonforte has been kidnapped by his political opponents, and his aides want Smith to impersonate Bonforte while they try to find him.
Bonforte is rescued, but he is in poor health due to the treatment inflicted on him during his imprisonment. This forces Smith to extend his performance, even to becoming temporary Supreme Minister and running in an election. (This is made plausible through Bonforte’s extensive Farley files. Similiar to a nomenclator.) The central political issue in the election is the granting of the vote to Martians in the human-dominated Solar System. Lorenzo shares the anti-Martian prejudice prevalent among large parts of Earth’s population, but he is called upon to assume the persona of the most prominent advocate for Martian enfranchisement. Smith takes on not only Bonforte’s appearance, but some aspects of his personality.
At the moment of electoral victory, Bonforte dies of the aftereffects of his kidnapping, and Smith assumes the role for life. In a retrospective conclusion set twenty-five years later, Smith reveals that he wrote the first-person narrative as therapy. Lorenzo has become Bonforte, suppressing his own identity permanently. He has been generally successful and has carried forward Bonforte’s ideals to the best of his ability. Penny (Bonforte’s adoring secretary and now Smith’s wife) says, “she never loved anyone else.”
The political system depicted in the book is a constitutional monarchy, with the House of Orange elevated to the role of providing an Emperor of the Solar System. The Emperor reigns (but does not rule) from a palace on the Moon, with the real power in the hands of a Supreme Minister, who must command the support of the Grand Assembly. Elections for the Assembly are held as in a Parliamentary system, there is an upper time limit (five years) between elections, but they can be called more frequently if the Prime Minister so decides, or if he is forced to it by the loss of a vote of confidence.
The United States is mentioned as initially having an unspecified associate status, and later obtaining full membership. In the system, the U.S. maintains full internal autonomy and is obviously a powerful voice in Empire affairs; Bonforte himself is an American.
The legislative power rests with a Grand Assembly, which also meets on the Moon (where the Imperial bureaucracy is located), most members representing an area of Earth or another planet, with other members representing constituencies not tied to any geographic place; one represents space pilots, for instance, and another districtless university women. As in the British system, representatives need not live in their district or be an actual member of the non-geographical constituency. Candidates for safe seats are determined by the central party office. At the time depicted in the novel, extraterrestrials are not permitted to be members of the Assembly, although they may vote in elections for representatives, and Bonforte has pledged himself to remove this exclusion. An afterword makes clear that he eventually does so, though his party subsequently loses power.