Harriman, a tycoon and latter-day robber baron, had always dreamed of going to the Moon, and had spent much of his career and resources making space flight a practical commercial enterprise.
Unfortunately, his business partners prevented him from taking the early flights because they could not risk the public face of their company.
Now an old man, Harriman has still not been to the Moon, a fact that frustrates him, since he lives in a world where space travel is so commonplace that carnivals have their own barnstorming spacecraft.
Very wealthy, Harriman bribes two spacemen to help him get to the Moon after encountering them at a funfair in Butler, a small town outside Kansas City, Missouri (and Heinlein's birthplace), where they sell rides on their old, somewhat run-down ship.
The three of them fight many obstacles, including Harriman's heirs, who want him declared mentally incompetent or senile before he can spend their inheritance.