In this comedy with musical numbers set in the Old South, Bing Crosby plays a singer (talk about a casting stretch!) from Philadelphia named Tom Grayson, who has fallen in love with Southern heiress Elvira Rumford (Gail Patrick). Tom wants to marry Elvira, but a man called Major Patterson (John Miljan) has announced his desire to do the same, and he challenges Tom to a duel to decide who will have Elvira's hand. Tom is not at all agreeable to this idea, which leads Elvira's father (Claude Gillingwater) to proclaim Tom to be a coward and deny him permission to wed his daughter. Elvira's sister Lucy (Joan Bennett), who is infatuated with Tom, thinks that he's merely being sensible, but Tom thinks that Lucy is too young for a serious relationship. In need of work and not especially welcome in the Rumford's community, Tom takes a job performing on a riverboat piloted by the blustery Commodore Orlando Jackson (W.C. Fields). One night, Tom finds himself in a barroom brawl with a man named Captain Blackie (Fred Kohler), who dies accidentally from a shot fired by his own gun. Hoping that his infamy will draw crowds, Jackson begins billing Tom as "The Singing Killer." Tom comes to realize that Lucy may be the right woman for him after all, but Lucy is not interested in a man with blood on his hands, and now Tom must convince her that he's not a killer at all. Noted gambling aficionado Fields has a hilarious poker-playing bit, and he steals most of his scenes from the rest of the cast. Mississippi was loosely based on the play "Magnolia" by Booth Tarkington.