Here are some important quotes from The Iron Heel by Jack London:

It cannot be said that the Everhard Manuscript is an important historical document. To the historian it bristles with errors—not errors of fact, but errors of interpretation. Looking back across the seven centuries that have lapsed since Avis Everhard completed her manuscript, events, and the bearings of events, that were confused and veiled to her, are clear to us. She lacked perspective. She was too close to the events she writes about. Nay, she was merged in the events she has described.

The frame of the narrative is an introduction by academic Anthony Meredith about the Everhard manuscript (which is the bulk of the narrative), written seven centuries before. Avis Everhard wrote the manuscript about her husband, Ernest, who tried to rebel against the Iron Heel.

We cannot fail. He has built too stoutly and too surely for that. Woe to the Iron Heel! Soon shall it be thrust back from off prostrate humanity. When the word goes forth, the labor hosts of all the world shall rise.

At the beginning of the novel, Avis Everhard predicts that the Second Revolt, which her recently deceased husband planned, will be successful. However, the reader knows, from Anthony Meredith's remarks that punctuate the narrative, that the revolt will be crushed.

“My father was a good man,” Ernest once said to me. “The soul of him was good, and yet it was twisted, and maimed, and blunted by the savagery of his life. He was made into a broken-down beast by his masters, the arch-beasts. He should be alive to-day, like your father. He had a strong constitution. But he was caught in the machine and worked to death—for profit. Think of it. For profit—his life blood transmuted into a wine-supper, or a jewelled gewgaw, or some similar sense-orgy of the parasitic and idle rich, his masters, the arch-beasts."

Ernest's motivation to rebel against the Iron Heel comes from the life of his father, which was, in Ernest's view, destroyed by work. His father's fate is why Ernest is so committed to helping the working class.

These things the oligarchs will do because they cannot help doing them. These great works will be the form their expenditure of the surplus will take, and in the same way that the ruling classes of Egypt of long ago expended the surplus they robbed from the people by the building of temples and pyramids. Under the oligarchs will flourish, not a priest class, but an artist class. And in place of the merchant class of bourgeoisie will be the labor castes. And beneath will be the abyss, wherein will fester and starve and rot, and ever renew itself, the common people, the great bulk of the population.

Ernest predicts that if the oligarchs succeed, they will built great cities that rival or surpass those of Egypt. These cities will be built (metaphorically) on the backs of the poor, who will exist in great numbers.

And through it all moved the Iron Heel, impassive and deliberate, shaking up the whole fabric of the social structure in its search for the comrades, combing out the Mercenaries, the labor castes, and all its secret services, punishing without mercy and without malice, suffering in silence all retaliations that were made upon it, and filling the gaps in its fighting line as fast as they appeared. And hand in hand with this, Ernest and the other leaders were hard at work reorganizing the forces of the Revolution. The magnitude of the task may be understood when it is taken into.*

These are the concluding words of the manuscript, and the editor, Anthony Meredith, writes that the manuscript was cut off in mid-sentence. Avis was likely captured at that moment (and later executed).