Macdonald Hall is losing all of their swim meets to rival school York Academy, which Bruno and Boots attribute to the school not having their own pool. After one meet, where the York Academy spitefully ignores the traditional handshake at the end, the two friends, after retaliating by dumping 20 lbs of effervescent solution into the pool, take this fact into account and ask Headmaster Sturgeon (aka The Fish) if there would be a chance at all of the Hall would be able to utilize its own pool, but he tells them the institution's fifty thousand dollars short of the cost of such a facility. Thus, Bruno, along with Boots, take things into their own hands. They start off with a flea market (without Mr. Sturgeon first knowing about it) and make $1426. After talking through the idea of fund-raising, Mr. Sturgeon allows them to pursue other means of making money and creates a bank account for them. This includes running a talent show, a photo-contest, and an Individual Effort Day. This is all in close cooperation with Ms. Scrimmage's Finishing School for Young Ladies, the girls-only school across the road. Their efforts in raising money are even more important when Boots reveals he might be transferred to York Academy because his parents think they have a better athletic program. After many fund-raisers, Mr. Sturgeon then tells them that they cannot gain any more money from the students and staff of the school because that isn't a reliable source of revenue anymore and if they want to raise money, they have to gain it from outside resources. Dejected, Bruno gets the desperate idea to set up a toll booth on a public road. Before anyone pays them, though, Mr. Sturgeon catches them, and after an awful encounter with Ms. Scrimmage and her students, punishes them severely and notifies them that they can't raise any more money. He also comes to believe that the pool they desire is borne out of jealousy of York Academy.
Eventually Mr. Sturgeon learns from a mocking phone call by the headmaster of York that many parents of his students are considering transferring students out of the school and into York Academy due to their better athletic program (mainly their pool), including Boots'. Realizing that the boys' attempts at raising money weren't a result of pure jealousy, but a fierce loyalty to the school and each other, he takes them off their severe punishment.
While complaining about never getting enough money, Bruno and Boots encounter George Wexford-Smyth III, Boot's wealthy old roommate. He tells them the solution, the stock market, and offers to invest their earnings under his direction. Although leery of this idea, the boys agree and George makes astute investments in a silver mining operation which then makes a spectacular discovery of a major supply of the element. As a result, the boys eventually sell the stock for $64,469.64, which is more than enough for the pool.