The "Good Old Days!" is the thirtieth episode of Season 5.
Mr. and Mrs. Turner are going out, but to Timmy's surprise, they are leaving him with Pappy instead of Vicky. Pappy is Mr. Turner's grumpy old father who hates everything modern and wants things to be like they were in the 1930s. After seeing one of Pappy's favorite old school violent cartoons, Timmy wishes he and Pappy into a 1930's version of Dimmsdale where twenty bucks makes them millionaires and targets of the evil Peg-Foot Vicky.
Timmy is asked to guess what his parents are gonna do and he says they'll go to a stupid place and leave him with Vicky. Dad says he's wrong, because Vicky is out spending time with her family. So they're going to a stupid place and will leave him with Pappy, Mr. Turner's Dad. A flashback shows Timmy's parents doing the same when Timmy was a baby. Pappy is reminded not to let Timmy suck his pacifier too much or he will get buck teeth. However as soon as Timmy's parents leave Pappy forgets even why he wasn't at his home. Back into present time Pappy says he doesn't like how things are nowadays in comparison with how they used to be when he was young. Pappy is a grumpy old man but as long as there is no animals biting Timmy's leg, no underwear on Timmy's head, and Timmy's head isn't in a toilet, Pappy is a better babysitter than Vicky, so Timmy will do all he can to convince his grandfather to agree about being his babysitter whenever he needed. Everything Timmy tries to impress his grandfather with results in Pappy saying something was better during his time than it is nowadays. Timmy then gives up and starts watching cartoons. Pappy says the cartoons from his days are better than the new ones. Timmy says that just because something is new it doesn't mean it's not good but after watching an episode of Captain Green and the Eco Teens, Timmy agrees this new cartoon is lame. Pappy then clicks on a channel, showing an old cartoon named Poke Eye the Longshore Man. Poke Eye eats some beets to become strong enough to beat a Bluto-like character.
The TV explodes after all that violence, and Timmy admits this cartoon is good, but Pappy says that now that the TV is broken, they can't see more cartoons. Timmy makes a sign and Cosmo uses his wand, starting a black-and-white segment. "Cosmo Presents POOF A Timmy Turner All Sound Wish:", a wand appears from the sky and dips into an ink holder, dropping globs of ink which form into Timmy, Pappy, and Cosmo and Wanda's 1930 versions. Cosmo and Wanda's disguises look similar to Foxy and Roxy of Looney Toons. Timmy said he just wanted to wish for a new TV. The Sun in the sky has a mouth and face, and warns people not to look directly into him or else they'll become blind. Pappy says back then everything was alive, including the wands held by these two "foxes" (Cosmo and Wanda's cartoon forms). As in cue, the wands flee from Timmy's Fairy Godparents, who go after them while Timmy and Pappy make a tour. Pappy warns Timmy about the dangers of old cartoons like almost getting hit by falling objects and luckily surviving, walking distracted through a construction site while ironically facing them. They go to a bar where they start spending the twenty dollars Timmy's parents left for pizza. Because in the days of the old cartoons twenty dollars can buy more than nowadays, so they can enjoy it even more. Things start going wrong when Peg-Foot Vicky spots them in the bar, and seeing them dressed up like millionaires, assumes they are rich and she kidnaps Pappy to steal the money. Vicky tries to tie Pappy in a railroad but the old cartoon styled villains who already have tied damsels in distress there say there's no place for more victims so Vicky drags Pappy to the abandoned saw mill. She ties Pappy to a log and starts the machine that saws logs into half. The machine is too slow, and Peg-Foot Vicky realizes why the place is abandoned and unused by the other villains. Timmy arrives but not only he fails to save Pappy but Vicky also grabs the money.
Cosmo and Wanda recover their wands and find Timmy, who wishes for beets and gets Poke Eye Brand Beets that turn him strong enough to save Pappy and defeat Vicky, but before Timmy does the former, Pappy tells him they cannot beat girls in old cartoons so Timmy wishes Peg-Foot Vicky was a man (the only visible change is that now Peg-Foot Vicky no longer has a ponytail) and beats "him". Peg-Foot Vicky runs into the sun and gets blinded, The Sun chuckles replies he warned them. Timmy wishes all to be back to normal. A POOF sign reading 'So Long, Folks' appears and the cartoon is no longer black-and-white after that. Timmy's parents come back and Pappy says he enjoyed the night so much he would babysit Timmy whenever he was called. Timmy was happy until Pappy tells all that happened, resulting in Timmy's parents saying they would no longer call Pappy for a while. Timmy and Pappy end this story sharing one last finger dance. Timmy also realizes that just because something may be old that doesn't mean it isn't cool which Cosmo relates. Wanda was, at first, flattered but became dismayed.