"The Mystery of the Riverboat" while ending each chapter with a cliffhanger is more episodic in nature than the usual Universal serial and somewhat similar to Universal's 1934 "Tailspin Tommy" in that aspect as some plot lines are completed as a story within the overall story. Plus, while some serials often contained a title song or motif throughout, this one has six songs scattered around and about performed by either Marion Martin - and we have no idea if she was dubbed or did her own warbling - and former Three Mesquiteer and future head Mouseketeer Jimmie Dodd, who did his own. The overly-plotted (for juvenile Saturday matinée audiences to keep up with over a period of 13 weeks) story finds three Louisiana families, the Langtrys, Perrins and Duvals, as co-owners of swamp land in the Louisiana bayou country. Unaware that the property contains rich "nitrolene" deposits, they are considering an offer from speculator Herman Einreich, who is well aware of the secret, having killed the scientist who discovered it and stolen his geological maps and notes. He boards a river boat, "The Morning Glory", heading for Duval's Landing. Others on the boat are the skipper, Captain Ethan Perrin, his daughter Jenny; Steve Langtry; Rudolph Toller; Bruno Bloch and Louis Shaber who represent a foreign faction also interested in the land; and a bearded man named Clayton, who is really the disinherited renegade son of the Duvals, Paul Duval, who thinks his brother Jean has cheated him out of his share of the Duval estate and going home to get even. With the aid of Batiste, "Clayton" murders Einreich, steals his maps and almost kills Steve and Jenny, who are saved by Napoleon, ship steward and Steve's friend. The Toller gang, assisted by ship entertainer Celeste Eltree, and headed by Rudolph Toller, pin Einreich's murder on Steve, who heads for the swamps at the end of chapter six, where he encounters some hostile Cajuns in Chapter 7, and ends up in a jail that ends up floating down the river when the levee breaks. But there are still six chapters to go, with lots of plot left, including chapter 12, where Steve, in a twist from the usual serial hero, manages to blow himself up as opposed to the villains doing it for him.