Dr. Leonard Gillespie, racing against time in his battle with melanoma, is about to start an important research project at Blair General Hospital to improve the use a Sulfa drug, Sulfapyridine, as a cure for pneumonia with the help of his assistant, Dr. James Kildare.

Paul Messenger, a Wall Street tycoon, asks for Gillespie's help in diagnosing the drastic, sudden personality changes that occur in his daughter Nancy.

When Gillespie collapses from exhaustion, Kildare forces the cranky old doctor to take a rest as a patient and persuades Blair head of hospital Dr. Carew to assign him to work full-time on the Messenger case.

With the help of ambulance driver Joe Wayman and his trusty monkey wrench, Kildare gets access to Nancy, who now has hysterical blindness.

Following Gillespie's advice, Kildare pretends to operate on Nancy's eyes and arranges for the first person she sees afterwards to be her fiancé, thus curing her hysterical blindness.