The show opens in the city of Duckburg, where Scrooge McDuck is swimming in his three cubic-acre vault of cash. He is forced to stop, though, by the realization that he is late for something. So, with a quick change out of his swimsuit and into his normal attire, he makes his way to the pier, where Donald Duck, now enlisted in the Navy, is preparing to ship out. As Scrooge arrives, Donald is saying goodbye to his nephews, Huey, Dewey and Louie, leaving them in the care of Scrooge while he's away. The boys are not very keen on staying with Scrooge for an indefinite period, and Scrooge is not keen about the idea either, but Scrooge is "the only one [Donald] trust[s]" with watching the kids. After Donald leaves, Scrooge brings the boys to his mansion, where he introduces them (and the viewers) to Duckworth the Butler. The boys are forced to have their meals sent to them in the attic, and receive a letter from Donald about his "adventures" in the Navy. After reading the letter, the boys manage to get out of the attic to fool around the mansion before Scrooge decides to leave for his Money Bin. Duckworth has firm orders to not let the kids leave the mansion, but the boys tie him up with a curtain sash ("This is definitely going to delay dinner"). Scrooge reluctantly allows the trio to hang around his bin, provided they don't touch anything. Scrooge tries to get the boys off his mind by kicking out solicitors. Among them is the leader of the Junior Woodchucks, whose offer Scrooge shows interest in. Just then, the nephews get ahold of a small wooden ship in Scrooge's museum that they thought they could send to Donald. Infuriated, Scrooge has them grounded.
Meanwhile, three of the Beagle Boys: Big Time, Burger and Bouncer manage to escape from jail using bombs that were sent to them disguised as bonbons. They then meet with El Capitán, the person who sent them the bombs, in the abandoned O'Lorange Theater. El Capitán, an anthropomorphic dog in a trench coat, arranged their escape because they are experts on Scrooge's Money Bin, and he wants them to steal a small wooden ship from it. The nephews, upset with Scrooge punishing them, decide to run away, but happen to notice El Capitán on the streets. They also notice the Beagle Boys in the Money Bin and run in to investigate. They fail to stop the Beagles from stealing the model ship, but the criminals end up leaving behind a map of Scrooge's Money Bin drawn on the back on a theater flyer. Scrooge comes in, having been awakened by the alarm; the boys try to explain what happened, but he refuses to believe them, thinking that the kids are the only ones who were interested in stealing the little boat. Luckily, the nephews figure out that the theater advertised on the flyer is where the Beagles are hiding out, and, thanks to the Junior Woodchucks Guidebook, they construct a hang glider to get out of the attic.
Afterwards, they head for the O'Lorange Theater, where they find El Capitán and the Beagles discussing the boat. According to El Capitán, it is actually a map that leads to a sunken treasure ship full of gold, and he is the only one who can interpret the code. The nephews nab the ship and escape, figuring that Scrooge will help them. The Beagles chase the trio all the way to Scrooge's candy factory, where Scrooge himself is answering questions for an interview, which eventually causes him to admit that he's grown fond of those pesky nephews. The two trios crash in, and Scrooge's nephews explain what's going on. A food fight breaks out, which eventually results in the Beagle Boys being covered in chocolate and sent back to the jailhouse. Scrooge apologizes to his grandnephews for not believing them earlier, realizing that this odd map may have something deep to it. El Capitán, meanwhile, swears revenge.