Donald has to do all the house chores until Huey, Dewey, and Louie return from a Junior Woodchucks meeting. When he's sleeping, a little Duck Avenger awakens him and escapes through the window. then the small Avenger appears at Donald's room door and Donald follows him outside, but the small Avenger then surprises him from the other side of the backyard. Donald doesn't understand how could he find his own alter ego, and in three places at once, but dismisses it as a stress-induced hallucination and goes back to sleep.
The following morning, Donald goes to see a doctor but Gyro Gearloose stops the 313 using his new invention, the Ultrasonic Tele-Brake, which uses ultrasounds to stop any mechanism in a one kilometer ratio. Then he gives it to Donald as he invented it just to test a theory. Donald continues his way and finds a crowd of kids buying Duck Avenger costumes. Donald is angry of having a seller taking advantage of the Duck Avenger's image while Scrooge McDuck is only slightly disappointed of not having thought it himself before such seller, but he gets really angry when he finds the seller is John D. Rockerduck.
Donald and Scrooge criticize Rockerduck, and Donald asks him why isn't he afraid of the Duck Avenger's retaliation, but Rockerduck laughs at it. Donald notices some of the kids are Junior Woodchucks and finds the meeting ended one day before, so he deduces his nephews were the small Duck Avenger pretending to be one at three places. Donald returns home where the kids pretend to have just arrived, but he finds their Duck Avenger costumes, which Rockerduck gave them for a small advance plus a future debt. Donald punishes them by having them clean the backyard and make dinner.
At night Donald, as the Duck Avenger, goes to Rockerduck's mansion, reaches the roof using his propeller belt and cuts the lights with the Ultrasonic Tele-Brake. Inside, he finds Rockerduck's secretary who tells him his boss is in the factory getting new costumes by train while he counted the earnings. The Duck Avenger shoots him with a paralyzing liquid, which actually is orange juice but the secretary gets a psychosomatic paralysis, and the Duck Avenger leaves with the money.
The Duck Avenger uses the hover function of the 313-X to reach Rockerduck's train that is already returning as it's an electric train. The Avenger uses the Ultrasonic Tele-Brake to stop the train and ambushes Rockerduck, who is treathened to write a declaration. Back at home, Donald changes to his normal clothes and leaves the declaration under the front door.
The following morning, a Sunday, the kids find the declaration and give it to Donald. Meanwhile, Scrooge has fabricated his own Duck Avenger costumes to compete with Rockerduck, but finds Donald giving Duck Avenger costumes to the kids and returning them their money, while Rockerduck eats his own hat. As an explanation, Donald gives Scrooge the signed declaration saying that Rockerduck promises to give the costumes as a gift to the kids, to be handed by the Duck Avenger's close friend Donald. Scrooge wants to beat Donald as he has ruined his chance to sell, but the kids defend Donald throwing snowballs to Scrooge. All Duckburg kids raise Donald over their shoulders while Scrooge and Rockerduck fight and insult each other.