Ed and Eddy are in Edd's kitchen, helping Edd carry in his family's groceries. Well, maybe "helping" is the wrong word, as what they are actually doing is playing with the food to get the food they want and generally wrecking everything. Edd complains and tries to get their attention so that they'll quit messing up his family's stuff, but this is to no avail, especially when Eddy grabs some broccoli and threatens Ed with it. Naturally, Ed can't stand the taste of broccoli, and he tears out of Edd's house by way of the screen door with Eddy in hot pursuit.
The chase runs through the Cul-de-Sac, causing much chaos for everyone. This includes Ed accidentally squishing Sarah and Jimmy with a painting Jimmy painted of a unicorn on a fence, Ed and Eddy destroying Rolf's eggplant garden, the duo wrecking Kevin's bike, and Ed accidentally stealing Plank. Eventually, though, Eddy catches Ed and threatens him, causing Ed to smack Eddy's hand with Plank. This sends the broccoli flying backwards, and when Eddy admits that the hit was painful, Ed apologizes and tosses Plank away–only for the broccoli to land in his hand. Ed now has the upper hand, and it is filled with broccoli that he plans to make Eddy eat.
Edd, meanwhile, has been chasing his friends, and has tailed them to that exact street corner. As they rush away from him, Edd tries to harangue them, but he doesn't get very far before Plank lands in his hands. Naturally, Jonny demands his pal back, and when Edd hands the board over, Jonny mentions that if he weren't so peace-loving, he'd commit some act of violence. Edd has no time to get used to this before he is accosted by Rolf, who blames him for the destruction of his eggplants. Before Edd can apologize, an equally peeved Sarah shows up with a suffering Jimmy, also blaming him for the actions of his friends. Kevin then walks up to him and delivers an ultimatum: get his friends to quit destroying everything, or they'll destroy him.
When Edd finds his friends, he sees Ed running around a tree, having been tricked into it by Eddy. Edd has his hat twisted into a knot, and he tells Eddy that Kevin threatened to tie his legs into the same shape if his friends don't stop their destructive actions. Eddy doesn't take Edd's complaints seriously, so Edd pretends to have accepted this, and warns Eddy that when he next sees his friend, Edd will be in the freak show as the boy with the pretzel legs, no salt. Hearing this, Eddy feels guilty, and he gives in to Edd, inadvertently playing right into Edd's hands.
As the first part of their training, Edd is feeding his friends soup. At first, it doesn't seem as if this will have any effect, but soon he reveals a method to his madness: he has taped bandages to the back of his friends' heads, and every time they misbehave, he'll rip one off. Soon, Ed has lost five bandages, and Eddy three due to various misbehaviors, but by now the training is starting to sink in, and the duo act polite, with Eddy offering to wash the dishes and Ed wanting to help.
With his friends totally reformed, Edd decides to show them off to the rest of the cul-de-sac, and he takes them out on the town. The first one they pass is Jonny, who has gotten a kite stuck in a tree, and it's here that the first signs of trouble manifest themselves. While Edd and Eddy pass him jovially and greet him politely, Ed stays to chat, and when he hears about the predicament, he is of course willing to help. Unfortunately, Ed's way of helping ends with him biting off part of the kite, rendering it useless and Jonny highly displeased.
Edd doesn't notice this, however, as he'd rather show Eddy off to Rolf. When they find him, Rolf is washing clothes, and Eddy starts helping out. At first, Rolf suspects a scam, but when Edd reveals that it's not an act at all, Rolf is pleased. Soon, though, he becomes quite uncomfortable, as Eddy has taken him and started to wash him as well. Eddy's excuse is that you could smell Rolf a mile away, and Edd swallows this, believing his training has gone too far. Fearful, he rips a bandage off of Eddy's head, but the message Eddy gets from this is that he missed a spot, and he starts to wash Rolf harder.
Before Edd can expend much more attention on Eddy, he is distracted by Ed, who has taken Kevin and begun brushing his teeth. Edd runs over to stop his wayward friend, but before he can have any effect, he hears cries from Jimmy, who has had his shoes tied by Eddy with his retainer and hair. Edd rushes over to help Jimmy, but before he can get Jimmy untied, Rolf angrily taps him on the back. Soon, the other angry kids (including Nazz) surround Edd, demanding justice. Thinking quickly, Edd escapes and hides, but he won't be alive for long, as there's an angry mob after him.
Edd's only hope is to stop the rampage of destruction his friends are committing. When he finds Eddy, he tries to get Eddy to realize the error of his ways, and Edd even admits that he was wrong in trying to change his friends. Eddy doesn't get it, however, and he simply keeps ripping up a flower garden (in order to get rid of what he deems "pesky weeds") and then perches Edd on a stick before leaving to do more good deeds.
By mid-afternoon, Edd has given up and is just sitting morosely on his porch steps. His friends come by and ask if they can help, but Edd just tells them to go away. Soon, though, they begin cracking jokes about helping, and eventually reveal that it was all an act. Angry, Edd goes inside, and when he comes out he has a piece of broccoli in his hand. Scared, Ed and Eddy run for it, along the way wrecking Kevin's bike again. Upon seeing Edd with the broccoli (who immediately shuts the door), Kevin went up to his door to give something to him, and that something, is his handlebar for a beating.
Sarah and Jimmy were both rammed into the fence by Ed. Strangely, Jimmy is the only one shown injured.
Towards the final scene, Ed crashes into Kevin and his bike. Following this, Kevin appears completely fine without injury. As Kevin approaches Edd, Kevin appears quite injured.
The episode's title is a reference to the famous musical My Fair Lady, in which a distinguished professor tries to pass off a Cockney flower girl as a princess. The plot of this episode also bears resemblance to the musical, as Edd tries to reform Ed and Eddy into respectable members of society.
Edd yelling "Not the screen again, Ed!" refers to when Ed destroyed Edd's screen door in "Button Yer Ed."
Edd explains Eddy's changed behavior to Rolf by stating "a little Pavlovian training has turned Ed and Eddy into upright fellows!" This is a reference to the work of a Russian physiologist, Ivan Pavlov, who used dogs as test subjects in his rather unconventional experiments when studying classical conditioning.