Huey, Dewey and Louie have set up their own lemonade stand outside McDuck Manor, and have employed Doofus to help them. Although the lemonade is cheap, it tastes quite lousy, and Doofus drinks the rest of the pitcher. Webby wants to help, but the nephews tell her off. Scrooge comes by to see how the boys' business is doing, but when he learns that they've invested six dollars and have only grossed fifty-six cents, he tries to give them a few cost-cutting pointers.
While taking a walk through Duckburg, Magica overhears Scrooge pondering about how his nephews will run McDuck Enterprises once they're in charge. Magica dresses up as a fortune teller, and offers to look into the future for Scrooge, but when she does, she is unable to get a clear reading (on purpose). Instead, she offers to send Scrooge himself into the future, using the Sands of Time from a mystical hourglass. After telling Scrooge that he can return to the present by taking the subway, which she claims is more efficient in the future, Magica sprinkles some sand on him, and whisks him away. With Scrooge no longer in the present, Magica gets ready to steal his Number One Dime.
Scrooge arrives in Duckburg, forty years into the future, and right away he wants to visit McDuck Enterprises, but a man tells him that the company is now called Magica-McDuck Enterprises, and that he can get there by taking any bus. Since a bus ride costs five-hundred dollars, Scrooge decides to walk, but not without learning that Magica-McDuck Enterprises runs the bus service in Duckburg.
Upon arriving at Magica-McDuck Enterprises, Scrooge is forced to pay one-hundred dollars just to enter the front door. Scrooge finds Miss Woods, the secretary, and learns that since today's payday, everyone must turn in their paychecks back to the bosses, which is apparently a privilege tax for working for Magica-McDuck. Huey, who is now an adult, videophones Miss Woods and asks if his and his brothers' lunches are ready. Scrooge finds a way to get a hold of the caterer's uniform (we never see how), and brings the nephews' lunches to their office.
Scrooge is thrilled to see his nephews all grown up, but they don't recognize him anymore. Instead, they've grown up to become ruthless businessmen. Scrooge asks why the boys have gotten so greedy, and they explain that forty years ago, Scrooge gave them some pointers at their lemonade stand, and that nobody's seen Scrooge since Magica got a hold of his Number One Dime. Scrooge insists that they need to get the dime back, but the boys are convinced that he's just some crazy old man, and ask Miss Woods to call the police.
Scrooge flees from the building, and realizes that he needs to return to the past to stop Magica from ever taking his dime. He tries to take the subway back to the past, but realizes that it was just a hoax. Scrooge then remembers that Gyro has his Time Tub, and heads over to his house to pay him a visit. Gyro, who is now old and senile, doesn't recognize Scrooge, but agrees to help him anyway. Since the Time Tub is now a birdbath, Gyro attempts to rebuild it, but the Time Tub only ends up flying through Duckburg, taking Scrooge along for the ride, and alerting a robot policeman. The Time Tub crashes in on a much older Launchpad, who's giving a crash course in flying. Unfortunately, the robot policeman catches Scrooge and arrests him for speeding and unauthorized use of a birdbath.
Now in jail, Scrooge demands to get to make a phone call, and the robot agrees to let him make one. Scrooge calls an operator, who tells him to deposit four-hundred dollars for the first three minutes. After being swindled robbed of four-hundred dollars, Scrooge asks that the operator tell his nephews that their Uncle Scrooge is in jail. To his surprise, the operator happened to be Webby, and she shows up at Scrooge's cell with Doofus. The two ducks apparently grew up into good looking adults who are now a married couple. Doofus bails Scrooge out with his and Webby's life savings, and Scrooge demands that they try to get his dime back.
Doofus takes Scrooge and Webby over to Magica's office in his helicopter/car, where Scrooge demands to see Magica, but the automated gatekeeper denies him access. Scrooge explains who he is, and the gatekeeper remembers that Magica is expecting him, so he's allowed in. A robot guard directs Scrooge, Webby and Doofus to Magica, whose head appears in the form of a large hologram. Magica explains that she took over Duckburg once she got her hands on Scrooge's dime. Scrooge tries to get the dime back, but Magica blasts him, Doofus and Webby with magical energy beams that teleport them into a dungeon.
Doofus uses his beeper to contact Launchpad, who rescues them by crashing his hovercar into the dungeon wall. Scrooge notices that spare parts from a robot guard are being dumped out of the palace from a garbage chute, so he dresses up in some parts and (poorly) disguises himself as a guard. The disguise gets Scrooge into the building, where he slips into a supply room. Scrooge dresses up as a salesman, and tricks the guard to Magica's room into letting him in. Scrooge then convinces Magica that she needs new alarms, and she tells him that Scrooge's her lucky dime needs more protection. Scrooge tries to take the dime and flee, but Magica sees through his disguise.
Scrooge gets chased through the building, and escapes outside through the garbage chute. Doofus flies himself, Scrooge, Launchpad and Webby away in his flying car, while Magica and the nephews follow in a jet, blasting them with lasers. The nephews overhear Magica mention Scrooge's name, and she explains to them that she was the one who made him disappear forty years ago. Although Doofus' car is about to crash after getting blasted, Dewey purposely crashes the jet next to it.
Scrooge tries to get a hold of Magica's hourglass, but Magica won't hand it over without getting the dime. Their fighting breaks the hourglass in half, and Scrooge tries to use some of the sand in his half to return home, but he accidentally sends himself and Magica back in time to an Ancient Roman colloseum. Magica tries to send them back herself, but they end up at a jousting tournament. Scrooge tries to use the sand a second time, but ends ups sending himself and Magica to General Cluster's Last Stand. Magica takes Scrooge's dime away, and accidentally sends the two of them forward in time on board the Zeppelburger blimp, which is about to blow up. Magica, who has run out of sand, begs for Scrooge to send her back home, but only if she returns his dime, so she parts with it, and they return to Duckburg, in their proper time.
Magica still wants the dime back, but Scrooge tells her that a deal's a deal, so she leaves him alone for now. When Scrooge sees his nephews practicing bad business habits for their lemonade stand, he scolds them for doing so. Scrooge then asks that the boys never go into business with Magica De Spell, even though they don't know what he's talking about. He then tells Doofus to take care of Webby and to invite him to their wedding. Webby, however, is grossed out by the idea of marrying Doofus. Scrooge then heads inside to take a nap, feeling like he aged forty years that day.