Gertrude Morel has an unhappy marriage to coal-miner Walter Morel in the English town of Bestwood. She is most devoted to her eldest son, William. Her second, sensitive son, Paul, grows up and works in a factory while painting on the side. William dies of a skin disease, and Mrs. Morel plunges into grief. Rededicating her life to Paul revives her, and the two become inseparable.
Paul, now a young man, spends a great deal of time with Miriam Leiver, a chaste, religious girl who lives on a nearby farm. Their Platonic relationship is intense and romantic, but they never approach physical intimacy. Mrs. Morel bitterly dislikes Miriam, feeling she is trying to take her son away from her. Paul grows attracted to Clara Dawes, an older, sensual woman separated from her husband. Finally, Paul and Miriam have sex, but he soon loses interest in her, unwilling to be bound to her in marriage or love.
Paul and Clara have sex and a romance blossoms, but her estranged husband, Baxter Dawes, savagely beats Paul one night. Mrs. Morel develops a tumor and, after a long struggle, dies. Paul arranges the reunion of Clara and Dawes, whom he has befriended since their fight. Paul and Morel move out of the house to separate locations. Paul feels lost, unable to paint any more. Miriam makes a last appeal to him for romance, but he rejects her. He feels suicidal one night, but changes his mind and resolves not to "give into the darkness."