A young doctor treats a gangster and falls for the man's kid sister.
Dr. Leonard Gillespie, the crusty senior physician at New York's Blair General Hospital, decides to teach his pupil, intern James Kildare, a lesson about dealing with the emotional causes of his patients' ills. To accomplish this, Gillespie fires Kildare and has him reassigned to work in the dispensary with nurse Mary Lamont, whom he orders to spy on the intern. On the day that Kildare begins his new job, Red enters the dispensary and asks the intern to help his injured friend. Kildare follows Red to the injured man, Nick Lewett, and discovers that Nick is suffering from a gunshot wound. Kildare is on the verge of reporting the incident to the police when Nick's enchanting sister Rosalie convinces him not to a file a report. Against hospital and police procedure, Kildare continues to treat Nick in a cellar hideout, even though he knows that the boy is wanted for the murder of bookmaker Bootsy Garson. Gillespie guesses what Kildare is doing, and tries to convince the intern to notify the police, but Kildare is so smitten by the flirtatious Rosalie, and so convinced of Nick's innocence, that he denies any acquaintance with Nick. An exasperated Gillespie arranges for Kildare's parents to call him home, but when the intern returns to New York, he visits Nick and is arrested by the police. For his involvement, Kildare is suspended from the hospital staff, but remains determined to prove Nick's innocence. Learning that Nick's visit to Garson was motivated by Tom Crandell's accusations that Garson had been maligning Rosalie, Kildare decides to visit Crandell himself. With the help of ambulance driver Joe Wayman, Kildare tricks Crandell into confessing that he killed Garson because of a gambling debt. After Nick is exonerated, Gillespie confronts Rosalie and forces her to admit that she was Crandell's girl friend and that her interest in Kildare was generated by her concern with her brother's welfare, rather than from affairs of the heart. Thus, a little bit wiser, Kildare resumes his life as Dr. Gillespie's assistant, and begins to look at Nurse Lamont in a new light.
