In his final "Mr. Wong" mystery, Boris Karloff solves the case of who killed shipping magnate Cyrus P. Wentworth (Melvin Lang). Wentworth's flagship "The Wentworth Castle" had tragically caught on fire with a tremendous loss of life. Near suicidal, the shipping tycoon is helped into the next world by persons unknown but dunderhead police captain Bill Street (Grant Withers) points the finger at Dick Fleming (William Stelling), the son of a rival tycoon and in love with Wentworth's daughter Cynthia (Catherine Craig). Promising to eat his hat if young Fleming isn't the killer, Street can only watch as enterprising cub reporter Bobby Logan (Marjorie Reynolds) assigns Mr. Wong (Karloff) to solve the case. Which the eminent Oriental sleuth does to the point where Bobby can gleefully add salt to Street's less than edible headgear. The burning of the fictional "Wentworth Castle" was actual footage from the infamous 1934"Morro Castle" fire, a tragedy that took the lives of 137 passengers.