Mr. Wong, Detective (1938)

In San Francisco, Simon Dayton, the senior partner in a chemical company, visits famed detective James Lee Wong as Dayton fears for his life stemming from a series of unexplained events in both his personal and professional life. But before Wong can meet Dayton at his office the next morning to follow up, Dayton is found dead in his locked office, the cause eventually discovered to be by poison. Captain Sam Street with the SFPD leads the investigation. The primary suspect is Carl Roemer, the scientist who developed the poison which he accused Dayton of stealing from him as he was never paid for the formula. One of the initial questions is how Dayton was poisoned behind the locked doors of his office. While Street takes the path of least resistance in the investigation in believing Roemer the obvious killer based solely on circumstantial evidence, more thoughtful Wong takes a broader approach in trying not only to discover other suspects, but how whoever the killer was able to administer the poison. Two of those other primary suspects are Dayton's partners, Theodore Meisle and Christian Wilk, who stand to profit substantially from Dayton's death, in addition to Dayton, Meisle and Wilk's many employees and associates. Adding to the investigation is Street's sometime girlfriend, Myra Ross, who nonetheless respects Wong's take on the investigation more than Street's in looking out for the proverbial little guy.