Dr. Leonard Gillespie and his assistant, Dr. James Kildare are about to undertake an important research project to develop a cure for pneumonia when Paul Messenger, a Wall Street tycoon, asks Gillespie's help in diagnosing the drastic personality change that has occurred in his daughter Nancy. Gillespie assigns the case to Kildare, who poses as an old friend of the family in order to observe Nancy. When Gillespie collapses from exhaustion, Kildare, fearing for his mentor's health, forces the cranky old doctor to take a rest by announcing that he is quitting the research project to work on the Messenger case. Kildare's announcement forces Gillespie to take a much needed vacation, and while the old doctor goes fishing, Kildare begins to investigate the causes of Nancy's symptoms. While visiting Nora, the family housekeeper, Kildare learns that Nancy has been suffering blinding headaches. Nora, who disdains all doctors, has convinced Nancy that she is suffering from the same type of brain tumor that killed her mother. Nora takes Nancy to see a nature healer named John Xerxes Archley, which prompts Kildare to admit that he is a doctor and dispute Archley's diagnosis. When the confrontation causes Nancy to go hysterically blind, Kildare consults with Gillespie over the girl's symptoms. Following Gillespie's advice, Kildare pretends to operate on Nancy's eyes, thus curing her hysterical blindness. Meanwhile, Gillespie returns from his vacation revived, and realizing that Kildare quit the experiment only out of concern for his health, reconciles with his assistant. Together they launch their research on pneumonia.