Life aboard a Mississippi shantyboat is poor but never dull for Jimmy, his younger sister Pigtail Anne, and their Uncle Al. Uncle Al has little money and holes in his socks, yet he makes sure Jimmy goes to school. Jimmy repays that devotion with fierce loyalty, even when it means refusing to run from danger.

Then a newspaper reports a mysterious flying object moving north over Louisiana. Soon Jimmy and Pigtail witness something enormous descend toward the river. Before they can make sense of what they have seen, an older danger arrives. The Harmon brothers have been feuding with Uncle Al, and this time they come prepared to settle the argument with guns and dynamite. As violence erupts on the water, Jimmy discovers that the strange object in the sky may be closer than anyone realizes.

The Mississippi Saucer appeared in the March 1951 issue of Weird Tales, when reports of flying saucers were becoming part of American popular culture. Frank Belknap Long places that new fascination in an unexpected setting: steamboats, cypress trees, fishing lines, shantyboats, and an old-fashioned river feud. The contrast gives the story much of its personality.

Frank Belknap Long had already been publishing professionally for more than twenty-five years when The Mississippi Saucer appeared. His first professional fiction appeared in Weird Tales in 1924, and his long association with the magazine included his celebrated 1929 story The Hounds of Tindalos. He also wrote John Carstairs: Space Detective, Space Station 1, Mars Is My Destination, The Horror from the Hills, and numerous short stories spanning science fiction, fantasy, and weird fiction. His professional career extended from the 1920s into the 1980s.