After getting kicked out of the Dimmsdale Demolition Derby and even the Dimmsdale dog park for bringing Sparky, Timmy mopes about how he is unable to take Sparky anywhere since he was only a dog. Wanting to spend more time with his magical dog, Timmy wishes that Sparky was a human, and Sparky becomes a regular boy with messy carrot orange hair and a bright star yellow shirt.
Unfortunately for Timmy, things don't turn out the way he wanted it to. Instead of Sparky spending more time with him, Sparky was actually becoming independent and going out and doing his own things. While Timmy is at home doing homework, Sparky is out having fun and seeing all the sights, and when he comes home, he raves about how wondrous it is to be a human being--then he throws up on Timmy's homework after pigging out on chocolates, a privilege dogs are not able to experience.
Seeing that he could not spend as much time with Sparky, Timmy wishes that Sparky was a dog again. Unfortunately, Cosmo and Wanda are unable to grant the wish because they could not interfere with true love, and Sparky was in love with being human; in order for them to turn Sparky back to normal, Sparky would need to agree to it first. To make matters worse, Jorgen Von Strangle appears and tells Timmy that by making Sparky a human, he has caused a mess in the human-dog continuum, and the only way to fix it is if Timmy takes Sparky's place as a dog, which is said in Da Rules. Now transformed into a dog, Timmy is given an hour to convince Sparky to become a dog again or else he would stay as a dog forever.
Cosmo, Wanda, Poof, and Timmy then poof to the Dimmsdale Demolition Derby. Unfortunately, they land in the demolition course rather than the audience bleachers, where several cars are dangerously targeting them. Cosmo and Wanda then poof to Sparky who is sitting in the stadium and inform him of what has become of Timmy. Feeling terrible for Timmy, Sparky agrees to become a dog again--after all, it was so uncomfortable to wear clothes. However, before Cosmo and Wanda are able to reverse the wish, Doug Dimmadome comes and grabs Timmy by the scruff of his neck, commenting that dogs were not allowed (yet again). Luckily, Mr. Turner got lost while driving and somehow ended up in the derby. Not wanting to hit a dining table which Cosmo poofed up during the panic, he swerves and hits Doug Dimmadome instead. With Doug Dimmadome out of the way, Timmy wishes for Sparky to be a dog again.