The Moon Is a Harsh Mistress is set, naturally enough, on the Moon, which the Earth government uses as a penal colony for irredeemable cases. Only those judged irredeemable are sent to prison on the Moon, because too long of a stay will apparently render an individual incapable of handling a return to Earth, due to the gravity differential. Having placed them on the Moon, the Earth government has the convicts hunt for water and set up wheat farms, the harvest of which is sent to Earth. This leads to a local economy of sorts, and to the interesting phenomenon of residents native to the colony as convicts have children. Further, as the various guards and administrators have to stay permanently if they stay too long, they often end up as de facto condemned life long prisoners alongside those who are de jure convicts. And because this mix of people have no way to return to Earth, a unique society grows up, straining at the restrictions imposed upon it from their distant mother planet.
Into this world Heinlein introduces Manuel, known as Manny, a native born on Luna who has grown up in this prison colony society; the agitator Wyoh "Wyoming" Knott-Davis, a woman transported to Luna as a child with her convict mother; and Bernardo de la Paz, a subversive professor deported to the moon as a political prisoner. To this mix, Heinlein also adds Mike, an accidentally sentient computer, who only seems to trust Manny, and, at the beginning of the book, has not revealed himself to anyone other than Manny. And from there the story, and the political, economic, and philosophical discussions flow. To tell the truth, the story itself - a tale of revolutionaries breaking away from their Mother country - is more or less just an excuse for the real meat of the book, which is the conversations between the characters as they talk about topics ranging from how families should be structured, to how governments should be created and run.
Some people dislike The Moon Is a Harsh Mistress, because they think the book should have been a snappy action oriented tale, and believe it to be bogged down by character interaction and philosophical musings. I view the book as exactly the opposite: With the characters and interactions as the featured element of the book, colored by a story of revolution filling in the margins. And because these conversations between the characters are so engrossing, this book is my pick for the genre novel with the most interesting character interactions.
Go to Day 20: What Is Your Favorite Genre?
Go to Day 22: What Genre Novel Sequel Disappointed You?