S.S. Van Dine's gentleman detective is reduced to an ordinary "hard boiled" gumshoe in this inexpensive mystery. Philo Vance (Alan Curtis) is hired by a magazine publisher, ostensibly as a technical advisor for a crime periodical. This is a cover for his "secret mission": to learn the truth behind the death of the publisher's former partner seven years earlier. When the publisher is himself killed, Vance learns that practically everyone who came in contact with the dead man had a motive. Vance gets to the bottom of things with the dubious help of his pretty secretary (Sheila Ryan). Philo Vance's Secret Mission was the fourteenth and final Hollywood film based on Van Dyne's creation.