John Ford's adaptation of the Sinclair Lewis Nobel Prize-winning novel stars Ronald Colman as the idealistic Martin Arrowsmith. Although a brilliant medical student, Arrowsmith's chances of pursuing a research fellowship are sidetracked by his marriage to nurse Leora Tozer (Helen Hayes). The couple returns to Leora's small Minnesota hometown, where Arrowsmith establishes a medical practice while continuing to do research on his own. After a few years, he discovers the cure for a bovine disease, which lands him a job doing research with former mentor Dr. Max Gottlief (A.E. Anson) in New York. Scientist Gustavus Sondelius (Richard Bennett), a friend of the researchers', informs them that a plague is devouring the West Indies. Eager to test a new serum, Arrowsmith accompanies the scientist to the islands, reluctantly taking Leora along. Although the white population refuses to participate in the experiment, a black doctor persuades the native people to take the serum. In the course of his research, Arrowsmith meets Joyce Lanyon (Myrna Loy), the daughter of a plantation owner--and finds himself irresistibly drawn to her.