It's the Nearburg "Parent's Day" festival, where all Nearburg residents celebrate with their parents, and CatDog, still not having to have found their parents, is feeling left out. Dog having so many theories on their own parents, still believes they are out there looking for them. Cat however, has lost all faith. But when Winslow tells them a story on the day he found them after a geyser tornado in Yonderland blew them into Nearburg, Cat is convinced to go to Yonderland on a parent hunt. Along their crazy journey, they run into many detours including an alien abduction, a giant lake monster, feuding hillbillies, and red, hot Peruvian fire ants.
Meanwhile, the Greaser Dogs decide to follow Catdog on their journey,
hoping to get the chance to beat up both Catdog and their parents.
Eventually, Catdog finds their way to Yonderland, where Dog is sad to find that their parents aren't there. Dog has decided to give up. But Cat, who wishes he was like as determined as Dog, convinces him that they will find their parents someday. More importantly, they will always have each other.
They suddenly meet a strange creature, at first thought of as a monster. It turns out to be both their parents, a frog and sasquatch. Catdog is only to be told they do not know where CatDog came from and that they are CatDog's foster parents. It turns out they were separated by a tornado when CatDog was a baby. Since then, they have searched for them, following every one of Dog's theories.
Suddenly, Winslow, the Greaser Dogs and many of the other characters they've met on their journey gang up on them. Luckily, Catdog are flown back to Nearburg by a tornado, along with their parents.