Scotsman Andrew Manson, an idealistic young physician, comes to the Welsh mining of Blaenely to work as an apprentice to Dr. Page. Life is hard in the town, and even Andrew must put up with adverse conditions when his employer's penurious wife forces him to work for a pittance and live in a small room. After Andrew saves the life of an apparently still-born baby, he becomes popular with the miners and their families. He also becomes close to Dr. Denny, a brilliant, but cynical physician who drinks heavily. When a typhoid epidemic breaks out in the town, Denny suggests that they blow up the foul sewage system to force the mine owners to build a new one, and Andrew assists him. Meanwhile, Denny has met Christine Barlow, the school mistress, and is attracted to her, but cannot approach her romantically. When Andrew hears about Aberalaw, a neighboring town that needs a new physician, but will only accept married men, however, he proposes to Chris. She accepts and both soon realize that they are in love. At their new home, Andrew begins research into the study of Black Lung Disease, an ailment that afflicts the miners. Andrew publishes his findings, which impresses the medical establishment, but disturb the people in Aberalaw who distrust his research and wantonly destroy his laboratory. Disillusioned by this reaction, Andrew decides to go to London to set up a practice in a poor part of London. Despite Chris's encouragement, Andrew soon becomes despondent over his lack of patients. One day, when Andrew is alone at his surgery, a shopgirl summons him to a fashionable dress shop where a wealthy young woman named Toppy Leroy seems to be having a seizure. Andrew slaps Toppy after he realizes that she is just hysterical, and scolds her for being pampered and spoiled. Toppy is attracted to Andrew and soon introduces him to her wealthy friends. By a chance meeting, he runs into Dr. Lawford, an old schoolmate of his, and Lawford suggests that Andrew join him in a fashionable practice. Soon Andrew is making a fortune treating rich patients who have little need of anything more than a pleasant bedside manner. He also begins to see Toppy, and Chris, who does not want all of the luxuries that Andrew can now afford to give her, becomes estranged from him. Even Denny, who comes to ask Andrew to work with him again, becomes disenchanted with the changed Andrew. Though he has been sober for some time, Denny gets drunk and tells Andrew what he thinks of him, then goes into the street, where he is hit by a car. Andrew then takes Denny to the hospital and asks one of the society surgeons he knows, Charles Every to operate to save his friend's life. Andrew assists at the operation and, though the procedure should be relatively simple, Every botches the operation and Denny dies. Andrew now begins to see the sham of his exclusive practice and realizes how he has changed. A short time later, Andrew learns that Anna Orlando, the young daughter of an old friend who owns a delicatessan, is ill with tuberculosis and has not been given the proper treatment at a London hospital. By happenstance, Andrew has recently become acquainted with Richard Stillman, an American who specializes in tuberculosis. Not a licensed physician, Stillman has earned the love and respect of his patients, but the ire of the medical establishment. Andrew takes Anna out of the hospital and has her moved to Stillman's clinic, where she is cured after undergoing treatment to collapse one of her lungs. Because of this, Andrew is threatened with the revoking of his license to practice medicine. At a tribunal before a medical review board, Andrew makes a plea to his fellow physicians to accept new ideas such as Stillman's, but the physicians are reluctant. As Andrew and Chris leave the hearing, they look toward the future together.