Dr. Leonard Gillespie, Lionel Barrymore, the crusty senior diagnostician at Blair General Hospital, clashes with his pupil, intern James Kildare, [Lew Ayres](/actor/lew-ayres, over a suspected case of Q fever. To teach him a broader lesson about the emotional as well as the physical roots of illness, Gillespie fires Kildare and reassigns him to a neighborhood dispensary, where he is to work under nurse Mary Lamont, Laraine Day, with the aid of head nurse Molly Byrd, [Alma Kruger](/actor/alma-kruger, who act as a training pair to keep him in check while watching his every move.
On his first day at the dispensary, Red arrives and quietly asks the intern to help his wounded friend Nick Lewett. Kildare follows Red to a cellar hideout and discovers Nick's gunshot wound. He is about to send Nick to Blair, but Nick's sister Rosalie Lewett, Lana Turner, pleads with him to keep Nick hidden for the time being. Against hospital procedure and the law that requires gunshot wounds to be reported to the police, Kildare chooses to treat Nick in the hideout, and he soon learns that Nick is wanted for the murder of bookmaker "Footsy" Garson. Rosalie's involvement complicates the situation, and Kildare begins to suspect that Nick's guilt may not be as clear-cut as it seems.
Despite Mary's misgivings, Gillespie uses her obvious sympathy for Kildare to push her to disclose what the intern is up to, and he warns Kildare that he is flirting with becoming an accessory to murder. He tries to persuade Kildare to reveal Nick's whereabouts, but the intern insists on Nick's innocence. To avoid jeopardizing his son, Kildare's mother is drawn into a plan that calls him home to help his physician father with a difficult patient; when he returns, he is arrested by the police along with Nick, and Kildare is suspended from Blair's staff once again. He remains determined to prove Nick's innocence.
Learning from Nick that he went to Garson after his friend Tom Crandell accused Garson of maligning Rosalie, Kildare confronts Crandell. With the help of ambulance driver Joe Wayman, Nat Pendleton and his own resolve, Kildare prevails and compels Crandell to confess that he killed Garson and shot Nick. After Nick is exonerated, Gillespie visits Rosalie and deduces that she was Crandell's girlfriend. She admits that her only interest in Kildare was to save her brother, and later confesses to Kildare that Gillespie had arranged Nick's arrest, though Kildare nearly ruined the plan by returning home. A wiser, more cautious Kildare resumes his role as Dr. Gillespie's assistant and begins to view Nurse Lamont in a more favorable light, recognizing the balance between medical duty and human compassion.
