The prize-winning novel of Sinclair Lewis was adapted by Sidney Howard in this story of a dedicated medical researcher.
Young Martin Arrowsmith (Ronald Coleman) is inspired by Dr. Gottlieb to pursue scientific research. He gets his M. D. and marries nurse Leora (Helen Hayes). She talks her family into giving him a start as a country doctor in South Dakota. As Dr. Gottlieb predicted, Arrowsmith seems to be a poor doctor; but he has great success finding a serum in an experiment to cure cattle of black-leg disease. Leora loses a baby and can have no more, enabling him to focus more on research. Arrowsmith joins the lab of Dr. Gottlieb in New York city, praying that God may keep him looking for his own mistakes and concluding, "God give me strength not to trust God." The director Dr. Tubbs publicizes his discovery as a way to kill all bacteria; but the exaggeration is useless when they find out a French doctor had already published a study.
The Swedish doctor Sondelius, whom Arrowsmith had heard speaking on medical heroes, inspires him to go to the West Indies, where the bubonic plague is raging. Before he goes, Dr. Gottlieb asks Arrowsmith to inject only half the patients for scientific reasons. West Indian authorities refuse to accept this, but a black Dr. Marchand offers him an island of suffering patients. Leora wants to accompany him there too, but he makes her remain behind for her safety. Arrowsmith and Sondelius inject half the patients, but Sondelius becomes ill and dies. Arrowsmith meets the married Joyce (Myrna Loy), whose role in the restored film has been substantially reduced by editing. He regrets he did not allow his wife to come and then returns to find she has succumbed to the plague. He gets drunk and gives the serum to all the patients, and he is credited with ending the plague by the British authorities. Back in New York Arrowsmith confesses to a collapsed Dr. Gottlieb that he betrayed science to be a humanitarian. Joyce offers him friendship, but Arrowsmith decides to leave the institute and do independent research with a colleague.
This story will inspire those inclined toward scientific thinking and idealists committed to humanitarian endeavors. Arrowsmith's enthusiasm and diligence are inspiring although his wife's sacrifices receive little consolation. The conflict between long-term thinking and short-term benefits is explored amid complexities of human relationships.