Timmy gets jealous when he sees how nicely Vicky treats her obnoxious, weenie dog, Doidle and wishes that he and the pooch could switch places. Poof! Timmy’s brain and the dog’s brain switch bodies. Two problems: One, since Cosmo and Wanda don’t speak dog, Timmy can’t wish himself back to normal. And Two, this is the day Vicky is taking Doidle to be fixed! Timmy must figure out a way to convince the dog to wish himself back to normal, before he ends up in the painful clutches of the fix-happy Dr. Snipowitz.
It is night time at the Turner's House, and Mr. and Mrs. Turner are going out of the house for the night. Vicky waves to them from the second floor window, while Timmy screams to them "No! Don't leave! Take me with you!". Vicky shoves Timmy down, and from Mr. and Mrs. Turner's vantage point, it looks like she is petting him and complimenting him. After Timmy's parents drive off, it is revealed that she is actually doing to this to her pet dog, Doidle. Timmy groans to Wanda and Cosmo that every time she brings Doidle over, she treats her dog better than him. Vicky hands Timmy a list of chores to do from his parents, but Timmy points out that it was in her hand writing and the tasks all involve Doidle. Vicky says her hand can also make a fist, and she tells Timmy to get moving. He is forced to walk Doidle in the pouring rain while holding an umbrella over him. Vicky calls Doidle in for dinner, while Timmy gets struck by lightning.
At the dinner table, Vicky places a juicy steak down on the dinner table in front of Timmy. He is about to eat it when she knocks him aside and tells him that it is for Doidle. Timmy is forced to eat a frozen TV dinner, which Doidle steals and eats from him as well, leaving Timmy with just the plastic to gnaw on. Later, Vicky is reading a magazine in the living room while Timmy is upstairs in his room, filing Doidle's nails. Timmy is fed up with being Doidle's dog, and wishes that he and Doidle would switch brains. Timmy's tiny brain is swapped with Doidle's larger one, just as Vicky enters the room and screams at Timmy to go to bed. Doidle, in Timmy's body, runs over to the bed, spins in a circle, and then lies down. Vicky happily greets Doidle (now Timmy) who leaps into her arms, and she carries him down to the living room. She tells Doidle to bark that he loves her, and Timmy begins to insult Vicky which she hears as barks from Doidle.
Vicky continues to spoil Doidle (Timmy) and let him do whatever he wants. He eats his own homework, and pees on Vicky's magazines. While he is eating ice cream and watching television on the sofa, Vicky says that he can do whatever he wants because tomorrow is his special day: the day Doidle is getting taken to the vet to get fixed. Timmy, still in Doidle's body, freaks out and runs to Cosmo and Wanda who are in their fish bowl. He tries to tell them what is going on, but they can only hear him barking. Timmy's parents return home, and Vicky drags Doidle (Timmy) off, leaving Cosmo and Wanda with the real Doidle stuck in Timmy's body. Wanda sends Cosmo to go follow Vicky and Doidle (Timmy) while she stays behind and watches over Doidle. Cosmo begins to tear up and doesn't want to be separated from Wanda, since they've never been apart since their wedding, but she reminds him they have to look out for Timmy first. Cosmo brags that he married the smart one, while Wanda cheers that she married the cute one.
At Vicky's House, she is tending to her pets: Happy the Goldfish, Chipper the Cat, and Ginny the Parrot, all of them who look like they've seen happier days. Chipper walks over to Doidle (Timmy) and asks if Vicky gave him a steak, laughing at him when Doidle replies she did and only making him more nervous. A flea bounces over to Doidle (Timmy), and he sees that it is Cosmo. Timmy tries to talk to his fairy godfather but Cosmo still can't understand him, and jumps on Doidle's backside to set up camp. Cosmo wants to call some of his old friends attempting to be optimistic, but he realizes that he has nobody to call, so as a result, he starts to cry because he misses Wanda. Back at Timmy's house, Wanda finally has time to write a romance novel for the ages. The next morning, Timmy's parents call him to breakfast, and Timmy (Doidle) excitedly scrambles into the kitchen yelling "Food!" over and over, burying his face into his bowl of cereal. His mother thinks he is just hungry, but his father says that is how all the kids are eating their cereal and tries to mimic it to be "hip".
The school bus pulls up and Timmy (Doidle) runs out of the kitchen to chase it. He gets to his school and starts to do weird things like sniff A.J.'s behind and drink from the toilet bowl. Francis walks into the boy's bathroom just then and Chester remarks to him that Timmy is tougher because he is drinking from out the toilet, so Francis starts to do the same to prove he is tougher. Chester and A.J. join in as well. Outside the school, Wanda is chatting with some of her Fairy friends in a tree, and they tell her that their godchildren switched places with animals too. One of the fairies says their godchild switched with a frog and Wanda remarks, "Don't they dissect those?" causing her friend to panic and poof away. Wanda decides to go check on Timmy. Chester and A.J. are wondering why Timmy is acting so strange, and Wanda gives chase to him when he starts going after a baseball.
At the Dimmsdale Veterinarian Clinic, Vicky and Doidle are waiting when they are called in by Dr. Snipowitz, who brings them into his surgery room where he shows Vicky all the horrible weapon tools he uses to fix pets. Cosmo notices that Doidle (Timmy) is about to get fixed and asks him why he didn't say something, getting a growl in response. Doidle bites Dr. Snipowitz's leg and he drops the snip-master 8000, breaking his leash and allowing Doidle to escape out of the window. Doidle sniffs around while Cosmo trails him, and points in the direction of Timmy (Doidle) with Wanda not far behind him. Cosmo calls over and waves to Wanda, so when she looks to smile back it causes her to crash face first into a light post, while Doidle and Timmy run into the entrance to Dimmsdale Park nearby. Cosmo happily rushes over and greets a dazed Wanda and asks her if she missed him multiple times and carries on to explain his day without her, but she grabs him by the throat and says she did. Inside the park, Timmy (Doidle) is chasing a ball when the real Timmy in Doidle's body puts his paw over it and confronts the dog. Doidle (Timmy) asks Timmy (Doidle) in barks to speak out the words to wish them back to normal, but Timmy (Doidle) refuses, saying that he can understand dog perfectly, and that he was just being a jerk, and wants to stay a human because he has opposable thumbs.
Doidle (Timmy) attacks Timmy (Doidle) while Cosmo and Wanda watch on. Cosmo is more concerned about talking about his and Wanda's time apart from each other, and gets jealous when she keeps talking about Timmy and not him. His jealousy gives Wanda an idea, and she transforms into a pretty poodle, causing Timmy (Doidle) to run over to her and start trying to pick her up. Wanda says that she has a toy bone for a real dog to chew on, but it can't be Timmy (Doidle) because he is just a boy with a silly pink hat, and she goes over to Doidle (Timmy) causing him to become envious. Timmy (Doidle) shouts out that he wishes that he was a dog again, and Cosmo and Wanda swap Doidle and Timmy back into their original bodies. Doidle, now back in his original body, barks at Wanda and tries to flirt with her, but she says that she is happily married and poofs away. Doidle beings barking angrily, but Timmy wishes for the dog to have a muzzle and be trapped in a small cage. Vicky finds Doidle squashed and helpless and brings him to the vet to be fixed.
That night, Timmy is watching television with an unhappy Doidle when Vicky introduces her new pet hamster, Spunky, and then feeds him a juicy steak. Timmy is about to warn Spunky about the implications of being very painfully fixed, but he calls greedily defends his steak, so Timmy says "He can find out on his own" and he, Cosmo, and Wanda laugh as the episode ends.