Dr. Andrew Mason (Donat) starts off his career as an idealistic doctor sent to the desperately poor coal mining towns of Wales to minister to the local miners. He does good work—reviving a child that seemed to have been born dead, saving a miner trapped under falled coal—but he refuses to issue work disability scrips for people who aren't really sick, thus alienating the locals. He also won't issue the placebo that less conscientious doctors were giving for tuberculosis, which frightens the ignorant miners, instead finding a link between coal dust and the onset of TB.
The miners repay his industriousness by throwing him out of town. Mason goes to London, but research into lung diseases doesn't pay the bills and he is reduced to poverty and doing ear piercings when he bumps into an old friend, Dr. Frederick Lawford. Lawford introduces him into the world of medicine for rich people, which in this case consists of bilking wealthy hypochondriac ladies with medical treatments they don't need for illnesses they don't have. Manson chucks his idealism and sells out, becoming wealthy, until the arrival of Phillip Denny, an old comrade from his days in Wales, reawakens a dormant idealism.
A young Rex Harrison has a supporting part as Dr. Lawford. Another future star of British screen and stage, Ralph Richardson (eventually Sir Ralph Richardson) plays Dr. Denny. Rosalind Russell pretends to be British as Dr. Mason's wife Christine; she has little to do besides look pretty and be his conscience in a couple of scenes.
- Birth/Death Juxtaposition: Right after successfully reviving a newborn boy, Manson walks past a funeral service for a victim of typhoid.
- Could Say It, But...: Denny has a very low opinion of Dr. Gribley, the district medical officer."I wouldn't have a word said against dear old Grib, except that he's a lazy evasive incompetent swine."
- CPR: Clean, Pretty, Reliable: The baby that Manson delivers isn't breathing. He slaps it on the butt a few times, but this fails. They put the child aside, only for Dr. Manson to change his mind and attempt revival by artificial respiration and dunking the baby in hot and cold buckets of water. Besides the fact that Manson should have done that immediately, the child is inert for a very long time before it revives.
- Death by Adaptation / Spared by the Adaptation: In the source novel, Manson's wife is killed in a traffic accident, and Manson starts a practice with his old friend Dr. Denny. In the movie, Christine lives but Dr. Denny is run over in the street instead.
- Dramatic Drop: Manson drops his glass upon finding out that his friend Denny has been hit by a car.
- Driving a Desk: Some terribly fake-looking shots while Manson is driving around.
- Good Doc, Bad Doc: Manson starts off as a crusading Good Doc, along with Denny, doing pioneering research on tuberculosis, but is seduced by the Dark Side and becomes a profiteering Bad Doc, scamming wealthy hypochondriac ladies with quack treatments for non-existent illnesses. It takes the return of Dr. Denny, and his death at the hands of a Bad Doc surgeon, for Manson to turn over a new leaf.
- Good Hair, Evil Hair: Manson grows a creepy pencil mustache after selling out and joining Lawford's corrupt practice.
- Hypochondria: The rich old ladies that Lawford and his fellow doctors are shamelessly bilking. Lawford has to yank Manson out of a room before he has the chance to tell one old lady that nothing's wrong with her.
- Indy Ploy: There's no money to repair the dilapidated sewer system that has contaminated the drinking water with typhoid, and the local government refuses to build a new one. So Manson and Denny blow up the sewer to force the government to build a new one.
- Obstructive Bureaucrat: The British medical establishment. They are horrified that Dr. Manson took a patient to an American named Stillman, because Stillman isn't a medical doctor—despite the fact that Stillman saved the patient when her British doctor would have let her die. For this Manson is brought up on charges that could lose him his license.
- Pretty in Mink: Andrew gets Christine a mink stole as they start moving up in the world.
- Riddle for the Ages: Dr. Manson walks out of his medical board hearing after his Rousing Speech, and the movie ends without revealing if he loses his license. In the novel, the board finds in his favor and he goes into private practice.
- Rousing Speech: Dr. Manson gives one at the end, excoriating the British medical board for ignoring non-doctors like Stillman instead of learning about the procedures that people like Stillman have developed.
- Time Passes Montage: Scenes of Manson working in London as multiple bills arrive, indicating that things are not going well.
- Title Drop: Christine describes her work with Andrew in research as "an attack upon the unknown, an assault uphill as though you had to take some citadel."
- Toplessness from the Back: Provided by Toppy Leroy, a society lady who is at Lawford's practice for a useless "irradium health bath".
- Trade Your Passion for Glory: The main conflict, as Manson, tired of being broke, leaves his idealism behind and starts bilking rich people.
- Worst Aid: After Dr. Denny is hit by a car, Dr. Manson directs the ambluance to his hospital and has one of his fancy surgeon friends perform the operation. Much to his horror, Dr. Manson finds out that his fancy surgeon friend is actually incompetent when said fancy surgeon botches the operation and kills Dr. Denny.