A little boy named Dickie Cessna, who lives at a country club where his father works decides to make some extra money by selling composted horse manure as fertilizer, and has his three sisters, Nene, June and Bette (two of which are older) join him in the enterprise. As their sales increase, they draw increased scrutiny from the IRS and state tax board, as well as the large scale competitor who seeks to put them out of business at any cost.
The children eventually fight a court case brought against them by the IRS. They are able to prove that the fertilizer is not taxable as tax had already been paid on the horse feed before the horses processed it into manure, removing one of the counts brought upon them. They eventually plead guilty to the others, which allows them to stay in business, to the consternation of the adult competitor.