Boris Karloff bows in for one last time as oriental detective Mr. Wong in the last of this long-running series. When "The Wentworth Castle" catches ablaze killing numerous people, shipping tycoon Cyrus Wentworth is distraught over the loss and is found shot to death in his office. Dick Fleming (William Stelling) is the prime suspect in the mind of the none-to-bright police captain Bill Street (Grant Withers). Dick is a business rival, and happens to be in love with Wentworth's daughter Cynthia (Catherine Craig). When cub reporter Bobbie Logan (Marjorie Reynolds) puts Mr. Wong on the case, the result is a foregone conclusion.