La Terre describes the steady disintegration of a family of agricultural workers in Second Empire France, in the years immediately before the outbreak of the Franco-Prussian War of 1870.

Buteau's father, the elderly farmer Fouan, has decided to sign a contract known as a donation entre vifs (literally: "gift between living people"), whereby his three children, Fanny Delhomme (married to a hard-working and respected farmer), Hyacinthe (aka "Jesus Christ", a poacher and layabout), and Buteau will inherit their father's estate early; they agree to pay their parents a pension in return.

Under "Jesus Christ's" influence, Fouan's self-respect dwindles: while previously law-abiding, he now joins his son on poaching expeditions and takes part in Hyacinthe's favourite evening activity, farting contests.

When Françoise turns 21 years old, she becomes entitled to her inheritance and she decides to leave the family home, demanding that Buteau and Lise buy out her share of the house, which the couple cannot afford to do.

While Françoise is still conscious when she is found, her family pride leads her to refuse to name Lise and Buteau; she claims instead that her injury was the result of an accident, and dies shortly after.

One night while Fouan is asleep, they steal into his bedroom and smother him; finding he is still alive, they set fire to him, while arranging the scene to look like an accident (their story is accepted by the local community).

La Terre picks up on a number of contemporaneous obsessions regarding the decline of France under the influence of the Civil Code, including lack of respect for father figures (hence the patricide which concludes the novel) and voluntary sterility to avoid excessive division of estates between numerous heirs (hence the infamous scene of "onanism", in which Françoise and Jean practise coitus interruptus to avoid conceiving a child).

But the novel also deals with more timeless themes: the parallel with the story of Shakespeare's King Lear emphasises the horror of aging and the physical and mental reduction which accompanies it.

In it, Zola's efforts to expose the unpleasant underside of his contemporary society reached its apogee; none of the other Rougon-Macquart novels features such sensational material.