Based on Honoré Morrow's novel, a preacher raises his son in a poor area; but his mother helps the son become a physician in the Civil War.
A steamboat brings minister Ethan Wilkins (Walter Huston), his wife Mary (Beulah Bondi), and their son Jason (Gene Reynolds) to the Ohio valley. At a meeting storekeeper George Ames (Guy Kibbee) proposes to reduce the parson's keep from $400 to $250, and this is accepted. Ethan socks two men for disturbing his sermon. Jason gets magazines from Dr. Charles Shingle (Charles Coburn), but his father won't let him keep them. George and Jim Meeker (Charley Grapewin) try to sell Ethan an old horse; but Ethan says, "Do unto others as you would have them do unto you." Mary sells two silver spoons so that she can get Harper's Monthly for Jason. The boy visits drunkard Dr. Shingles and borrows a medical book. A horse runs wild, and Ethan stops it. Mary gets him to buy it and name it Pilgrim. When Ethan learns that Jason has magazines, he spanks him. Jason sews a cut on Pilgrim.
After ten years Dr. Shingles says they should raise Ethan's salary and gets George to agree. Ethan takes Jason (James Stewart) on his circuit and tells him to be content with mush. Sister Clarke (Leona Roberts) gives Jason an old coat; but Jason complains and argues with Ethan. Jason refuses to be whipped and fights with his father. Jason is beaten and rides home. Jason tells his mother he is leaving and takes the steamboat to the Baltimore College of Surgery. Jason tells Dr. Lupus Crumm (Robert McWade) he will work under janitor Quid (Gene Lockhart). Mary gets a letter from Jason asking for money. Ethan is ill and offers to sell his father's watch. Jason eats with Quid and gets a letter to go home. Dr. Shingles cares for Ethan and tells Mary he is dying. Jason arrives and attends the funeral.
Three years later Mary gets a letter that Jason is not coming. Dr. Shingles gets a ring from George and gives it back to Mary. In the Civil War Jason needs money for a uniform and gets Mary to sell Pilgrim to the army. Chauncey (Sterling Holloway) takes over the store after George died. Mary has not got a letter from Jason for two years. Jason treats the wounded soldiers and is summoned by President Lincoln (John Carradine), who praises his work. Lincoln asks Jason how he paid for medical school and about his mother. Lincoln says Mary wrote to him. He lectures Jason on gratitude and makes him write a letter to her. Jason goes back and finds Pilgrim. Jason saves the arm of Captain Griggs (Minor Watson) and is given Pilgrim. Quid hands Jason his furlough papers, and Jason rides home to Mary. Jason asks her to forgive him. In the final scene Mary says grace as she and Jason dine with Annie (Ann Rutherford) and Dr. Shingles.
This masterful drama of human relations contrasts the spiritual values of Ethan to the more worldly yet humanitarian concerns of Jason, while Mary loves and supports both. Lincoln well represents the poignant concern for a long-suffering mother.