"Psycho Duck" is the fifty-second and final episode of The Proud Family.
Penny and her friends are out swimming in a lake when Penny notices a duck drowning over by a buoy. She rescues the duck and resuscitates him back to health after Dijonay declines.
Afterwards, Penny takes the duck, whose name is revealed to be Chester, over to her mother’s office. Trudy diagnoses Chester as an “Easter duck”, in which parents give baby ducks and chickens to their kids “not realizing the effect it will have on the animal” during the springtime. Fearful that animal control will kill him, Penny decides to take Chester home with her, much to the annoyance of Oscar, who develops a tense rivalry with Chester after he catches him eating his cobbler ("It's an evil duck!" he decries). Later that night, Oscar discovers that Chester ate his steak sandwich and tries to warn Trudy of Chester’s malicious actions. Instead, they find Chester sleeping in Penny’s bed.
Even after a few days, Oscar is still not phased with Chester’s visit, even after the duck saves him from chocking after he accidentally eats a plate of live worms. Penny soon discovers a more vicious side to Chester when he follows her to school, fights off the Gross Sisters and scares her friends away. Back home, she finds out that Chester took his anger out on Puff and the only thing that can calm him down are cartoons on the television. Penny tries to get onto Chester’s sympathetic side by offering him a plate of worms, but Oscar shows up with Bobby, Felix and Papi, demanding Chester to surrender the TV over to him. Chester, however, frightens his human occupants away with a well deserved roar.
Oscar devises a plan to get Chester out of the way by taking the whole family out to a picnic in Canada while Felix and Bobby kidnap Chester (and presumably kill him), but the plan goes awry when Chester fights back against his kidnappers, who crash their car into a truck offscreen. Bandaged, Bobby and Felix return home to report that Chester is gone, only to discover that Chester somehow followed them back and has now usurped control over the Proud Family house.
Days later, Penny takes Chester to the park where she reads to him The Ugly Duckling...for the fifth time. As Penny begins again, the two catch sight of Bobby in disguise as a swan, who lures Chester over to his raft. But Chester throws him overboard and escapes to safety on the raft. As Suga Mama jumps in to rescue Bobby, Penny tells her parents that Chester will forevermore be the last wild animal she brings home, but she quickly changes her mind when she sees a little white rabbit...that can talk in a deep, baritone voice.
In a pre-credits scene, Penny, Trudy and Oscar find out that Chester has been restored to his owner, and, to Oscar’s dismay, a million dollar reward was claimed by Wizard Kelly.
- This aired 30 minutes before the premiere of "The Proud Family Movie", part of "The Proud Family Pre-Show Party Marathon".
- Penny, Oscar, Trudy, Suga Mama and Dijonay are the only charatcers to be in all the episodes.