Based on the novel by A. J. Cronin, a doctor begins taking care of the poor and miners but gives up experiments to make money in London.
Dr. Andrew Manson (Robert Donat) arrives to assist elderly Dr. Page. Dr. Denny (Ralph Richardson) tells Andrew there is no hospital and warns of typhoid, saying they need a new sewer. Andrew goes to school-teacher Christine (Rosalind Russell) to insist she isolate a boy. Andrew delivers a baby that does not breathe until he bathes him. Andrew and Denny drink and blow up the leaking sewer to stop typhoid. Christine comes to Andrew with a sore throat. Andrew quarrels with Mrs. Page and gives notice. Andrew is interviewed by a mining society, but they want a married doctor. So Andrew says he is engaged. Andrew explains to Christine, who agrees to marry him.
Andrew and Christine move into a large house, and Andrew gets the microscope from Denny. Andrew refuses to certify a man who has not worked for years and finds five men with lung problems who are not let off work. When a man's arm is trapped, Andrew amputates before the mine caves in. Dr. A. H. Llewellyn (Joss Ambler) will not let Andrew see his chest cases in the hospital. Andrew tells Christine he will resign, but she suggests using his microscope. A nurse complains about Andrew's new methods and quits. Christine helps Andrew with his experiments. Andrew tells Owen (Emlyn Williams) that dust in the anthracite mines is the cause; but the men asks for their cards back. Christine cries and tells how men destroyed their lab and guinea pigs. Dr. Llewellyn suggests that Andrew give up his "hobby," and Andrew gives notice.
Andrew and Christine go to London, but bills cause him to sell his microscope. Andrew is taken to a hysterical woman, clears the room, and slaps her. Her sister asks him to their home, and Toppy LeRoy (Penelope Dudley-Ward) tells him to see a good tailor. Andrew meets old friend Dr. Lawford (Rex Harrison), who takes him to a nursing home and gives him five guineas for consulting. Andrew gives Christine a fur. Andrew plays golf with Dr. Lawford and Dr. Every (Cecil Parker) and gets money from the latter for assisting. Dr. Stillman (Percy Parsons) commends Andrew for his paper on dust inhalation. Toppy asks Andrew to come see her, and Christine reads of it. Andrew shows Christine their new car. Denny tells them of a clinic he is opening using health maintenance, but Andrew declines to join him. Christine tells Andrew that his work is bettering humanity, not making money. They find Denny drunk, because Andrew has become mean. After a car accident Andrew and Every operate on Denny, but he dies. Andrew tells Every that he killed him because of incompetence. Andrew walks in a daze and hears Denny's voice on a doctor's work. Andrew goes to help Mrs. Orlando's daughter Anna and risks his career working with Stillman. Every prosecutes Andrew before a medical board; but Andrew defends Stillman, making Christine happy.
This realistic drama contrasts the early struggles of a young doctor, caring for the poor, to the decadent practice of coddling the rich. Fortunately his wife values helping humanity more than having wealth, and he is able to realize his mistakes and reform.