Luna is an open penal colony and the regime is a harsh one. Not surprisingly, revolution against the hated authority is planned. But the key figures in the revolt are an unlikely crew: Manuel Garcia O'Kelly, an engaging jack of all trades, the beautiful Wyoming Knott - and Mike, a lonely computer who likes to make up jokes...
Even though this is one of his later novels, it feels much earlier. The classic Heinlein themes are there: fierce individualism/libertarianism, free love, pluralistic marriages, interesting extrapolation of scientific discoveries (AI) and frontier exploration (moon colonization), and quirky characters, male and female. But it feels stilted, not like a book that was written AFTER Stranger in a Strange Land or Starship Troopers, and just before I Will Fear No Evil, and over-elaborated at times (e.g, a 4 page diversion on the best way of organization revolutionary cells so a minimal number of people can be betrayed could have been done in a paragraph or two).
I enjoyed it, but I think there are better, easier Heinlein reads.