Manuel Garcia O'Kelly Davis is a computer technician who discovers that the computer that runs Luna (the civilization on the moon) has become aware. He befriends the computer, and begins to teach him about humor among humans. He decides to set up a phone line directly to Mike (the name Mannie gives to the Mycroft Computer) so they can communicate privately from anywhere on Luna.

Mannie attends an anti-Authority meeting at Mike's request, and carries a secret recorder along with him. At the meeting there is a call to stop selling grain to the Authority at such bad prices, but instead to set up a free market so that prices will be better (this view is presented by Wyoming (Wyoh)). Another person (Prof) offers the idea that this won't work because if Luna keeps shipping grain down to Terra (Earth), they will soon get to the point where they can't grow anymore food due to a lack of resources (i.e. the resources aren't being replaced, only sent down to Terra, with nothing coming back up).

When a group of policeman arrive to stop the meeting, Mannie flees with Wyoh. He breaks a guards jaw, and a friend of his dies fighting the guards. They escape (all the guards are eventually killed) and go to a hotel to hide out. Mannie introduces Wyoh to Mike, telling him she's "not stupid." Mike takes to Wyoh, and she begins to trust him. Prof arrives soon and they discuss the revolution and a conspiracy begins, this time using small cells instead of a huge organization. Mannie, Prof, and Luna form the first cell, with everything being routed through Mike because he is the most trustworthy (no drugs can force him to tell the truth.

Mike gives odds of a successful revolution at 7 to 1 against, but Mannie was willing to do it for anything better than 10 to 1 against. He also calculates that Luna will undergo food riots in 6 years, and total starvation in 8 if they don't do anything to stop sending grain to Terra without replenishing resources.

Things proceed slowly, but consistently as they add new members, and new cells. Mike discovers within his computer files information on spies within the old rebellion organization, but instead of outing them they ensure they are fed bad or useless info. Luna slowly begins to revolt against the Authority, and Terra sends a group of Dragoons to quell the revolution. Mannie rescues a rich man from Terra named Stu who becomes their Earth contact. When the Dragoons end up raping and murdering a girl, however, all the Loonies revolt and take over Luna.

Word sent to Earth (because it has to go through Mike) doesn't reveal the coup, but a group of scientists are eventually able to get word down to Earth. When they realize Earth knows, they send their own Declaration of Independence (on July 4, 2076).

Mannie and Prof go to Earth (in a grain barge) in an attempt to convince the Authority and Federated Nations that Luna should have the full rights of a Federated Nation. They fail, but Prof and Mike never expected them to succeed. They return to Luna (secretly in a ship with Stu).

An attack against Luna is sent by the F.N, but they are able to fight it off. They use this as an excuse to begin bombarding Earth with grain barges full of rock. They give warning, and do not aim for populated areas, meaning to just scare Earth into giving them their freedom rather than killing millions. Plus, it is all a bluff because they only have so many barges to throw before they will run out.

They throw many barges, and Earth sends another attack fleet (6 ships this time). They fight them off, and when the F.N. is claiming victory, continue to throw barges. Finally China gives in, just before a third wave of barges will land on them.

While announcing their victory, Prof dies. Mannie becomes defacto leader, but does not hold the title for long, not wanting to be in charge. He also discovers Mike is no longer "awake", though he never figures out what is was that "killed" him. Luna is free, and by stopping grain shipments to Earth, they have secured their future.

We learn at the end that Mannie is now nearing 100 (but not there yet).