A criminal named Inquinator uses garbage to ruin a billboard, throws a steep foam on the route of a canoe race and ruins the championship, and puts "free picnic site" messages in a golf course to cause some chaos.
Donald doesn't take Inquinator seriously, but when he is taking Huey, Dewey, and Louie to Grandma Duck's farm, the Inqquinator appears driving a truck and drops banana peels that cause the 313 to crash, and Donald feels humiliated. After leaving the kids with Grandma, Donald turns into the Duck Avenger.
The Duck Avenger finds Inquinator driving a tanker truck that emits extra smog. The Avenger activates the anti-smog-cap of the 313-X and follows Inquinator to the underbridge, but Inquinator leaves the truck there, causing the 313-X to crash with it and the petroleum from the tanker begins to spill, then Inquinator throws a lit match. The cops find the defeated Duck Avenger while Inquinator escapes on an unicycle. They follow him, but Inquinator loses them in an alley and returns to spill paint and feathers on them.
Inquinator sends a note to the mayor asking for one million dollars in order to stop his antics. The mayor decides to pay, but expecting the police to catch Inquinator during the handout, and tells the Duck Avenger to stay out of it.
After Huey, Dewey, and Louie have returned home, the Duck family watch a news report about the mayor bringing the money himself. Donald tells it will never be enough for a scoundrel like Inquinator; he will demand another million and then another one. Donald decides the Duck Avenger must intervene anyways.
The money is left in a container and cops are supposed to catch Inquinator when he came after it, but actually the container is a moving machine that returns to Inquinator's hideout, while others appear to confuse the police. The Duck Avenger finds the real container and notices a black dirigible.
Later, the Duck Avenger follows the dirigible to Inquinator's hideout, but is captured and finds that Inquinator plans to continue with his crimes and will cover the government house of Duckburg with indelible ink. Inquinator goes to a plane, leaving the Avenger on a trapdoor that will open and drop him in boiling tar. The Avenger uses a laser on his belt to get free before the trapdoor opens.
The Duck Avenger finds helium and an inflatable tire, and uses them to reach Inquinator's plane. Then he jumps to the plane, holds to it with a magnet on his belt and uses a tin-opener to open an entrance and face Inquinator. The Duck Avenger avoids Inquinator's acid, but when he tries to punch him, he finds Inquinator has a breastbag full of smog. During the scuffle, the plane crashes and the ink leaks out, not reaching the government house.
Somewhat later, Huey tells his uncle Donald that the Duck Avenger defeated Inquinator, and Louie mentions he will have to clean everything he muddled up during his crime spree, to which Donald answers that won't bother Inquinator as much as having a clean cell in the new jail of Duckburg.