Walter Mitty, played by Danny Kaye, a timid proofreader for a pulp magazine publishing company, often escapes his mundane reality through daydreams. He is approached by a woman named Rosalind van Hoorn, played by Virginia Mayo, for help in eluding a mysterious person who is following her. Mitty becomes embroiled in an international ring of jewel thieves, led by Konstantine Shayne, who are plotting to steal a vast fortune in gems from Rosalind's uncle. As he tries to aid her, the thieves make several attempts on Mitty's life, including one by a fake psychiatrist, Dr. Hollingshead played by Boris Karloff, who tries to push him out of a window. After Rosalind is captured, Mitty rescues her and takes down the entire ring in a series of comical and frantic chases.