The episode starts in Papa Smurf's lab where the Piximp is cleaning while Brainy, Clumsy, and Joey are bringing the ingredients for the Intelect potion. When Papa finishes, Clumsy trips and knocks him over, causing him to throw it out the window. He apologizes, so he forgives him; the trio decides to have a walk around the village while Papa Smurf remakes the potion.
In a pond not too far from the village, the potion is found by a Scorpomouse who drinks it, mistaking for something to quench his thirst. He sticks out his tongue and says, " Ew! What a terrible flavor!" He then realizes he can talk instead of executing squeaky noises - not only that, but now he is capable of thought.
Meanwhile, Greedy is baking a chocolate Smurfberry cake when Papa, Brainy, Clumsy, Joey, and the Piximp arrive. He has not yet met Joey, so he asks Papa Smurf, "Who is this Smurf? I've never smurfed him before." Papa he introduces them, and so Greedy offers him a slice of cake, to which Joey replies, "But I don't have any money!" Greedy assures him it's okay and Papa explains that Smurfs have no need for money. Shocked, the Piximp reacts with a stark, "Chaw?! You gotta be kidding!" Joey tastes the cake and loves it instantly.
As they leave, the Scorpomouse - now wearing a blue pork pie hat and green bow tie - appears at Greedy's side and asks him if he could give him a slice of Smurfberry cake. The Smurf does, but as he walks away, he realizes that he is making off with the whole cake, singing, "Listen to the Mocking Bird." Greedy grabs him and says, "What do you think you're doing to my chocolate - smurfberry cake, and who are you?"
He introduces himself as "Stingle" the Scorpomouse and demands, "Please let me go or else!" Greedy refuses, so he adds, "Okay, boss, you leave me no choice..." He stings Greedy's hand with his tail which makes him let go, but then he starts to feel bad and explains how his tail has a stinger that injects a deadly poison. He says, "I hate to say this, but I warned you!" Greedy races to Papa Smurf for an antidote against Scorpomice poison while Stingle proceeds to leave.
Later as he heals, Greedy sees Stingle eating the cake, so he starts to chase after him. He starts to drop globs of frosting which makes his assailant slip. Then he climbs onto a kitchen table and tries to get the cake, but Greedy grabs him by the tail and prevents him from using his stinger. Stingle grabs a frying pan and glares at Greedy, hitting him on the head, and runs when released. As he starts to gain on him, he grabs a Smurfberry and throws it at his face. Extremely angry, Greedy shouts, "Alright, no more Mr. Nice Smurf!" He takes a pot and dashes towards him.
Stingle attempts to escape, but it's too late - he's already trapped inside the pot and hears him say, "Now I'll smurf you!" to which Stingle replies, "Oh no, you won't," in a sing-songy fashion. Greedy answers with an, "Oh yes, I will," in the same tune, and recieves, "You'll be sorry!" Disregarding it, he puts his hand under the pot and something hits it, making him yell. Thinking he had been stung again, he leaves to drink another antidote potion; while he does, Stingle gets out of the pot and reveals a pin with a sharp point and snickers, "So long, stupid!" He takes the opportunity to escape after stealing the remainder of the cake.
When Greedy returns to the kitchen to finish some business with Stingle, he realizes that his cake is gone and pass out. Stingle says, "My, my - this wouldn't have happened if he had shared the cake with me." Then he enters the hole in the floor while singing, "Listen to the Mocking Bird," thus ending the episode.