Mr. Crocker builds a portal to Fairy World, but it instead turned him into goo. Denzel's mother Dolores-Day tells him he wasted his life chasing fairies (all the while, whacking him with a broom, even when he restores himself to normal). So he picked her up and froze her with a freezer gun. Crocker then goes to his wheel of destiny to find a new vocation. The first that comes out is Women, but Crocker says "Let's be realistic" and the wheel ended in leprechauns. He finds it the perfect fit, as leprechauns can't fly and isn't magical like fairies can and they have pots of gold. Because he can't go to Ireland on a teacher's salary, he instead settles for Little Ireland, an Irish-themed neighborhood in Dimmsdale.
There, Cosmo is telling his family about Leprechanuka, a holiday in which the Great Potato comes to give joy and happiness. Because Cosmo was dressed as a leprechaun, Crocker captured him and demanded gold, so Cosmo gave him a pot of gold. When he returns, Wanda tells him that he can't poof up gold, so he replies he took it from the McPunchies clan, a group of tough leprechauns. The McPunchies appear and demand their gold back. Timmy tells Big Dave (the leader) that Crocker has it, so his brothers Lucky and Greeny take Wanda and Poof while Dave, Timmy, and Cosmo go to recover the gold. It turns out that Mr. Crocker spent it all at a superstore called Big $tuff, and bought among the stuff, a talking car. When Timmy tells him Crocker needs the gold, Denzel replies that he spent it all, and Dave demands it back or else. Crocker attempts to leave, but Dave gives them until the end of Leprechanuka to recover the pot o' gold--after Timmy expresses surprise at learning that Leprechaunaka's a real holiday, he and Cosmo (along with Crocker) try various ways to make up for all the gold that Crocker spent.
The first thing they try is Cosmo and Timmy competing in a figure skating competing with Crocker as one of the judges--if Timmy and his godfather get three perfect 10s, they'll win the gold medal. While the first two judges give them perfect 10s, Crocker (out of habit) gives them an F, which earns him a glare from both Timmy and Cosmo--afterwards, they go to a gold mine, where Cosmo warns them of the eighth dwarf, Crazy, who is giant and attacks them with a chainsaw. The time ends and Dave takes Crocker to his realm. Timmy and Cosmo follow them and they are led to Ireland. Wanda and Poof were having a great time, eating Lucky Bits.
Dave returns and asks Greeny and Lucky to get him the human vaporizer, but they can't find it cause everything's green in Ireland. When Timmy and Cosmo arrive, Dave says he'll cook the four of them. Then Cosmo's belief in the Great Potato brought it to life, who scares the McPunchy-brothers into letting Cosmo and the others go. Timmy apologizes to the McPunchy-brothers about not being able to get their gold back, but Big Dave admits that they cared more about getting the pot back, as it's an old family heirloom (and, judging from Big Dave's reaction, apparently has a lot of sentimental value to them). The gang gives the cauldron back to the McPunchies and head back home, where Crocker decides against hunting leprechauns and to try hunting/obsessing over something else. The Wheel of Destiny initially lands on dwarves, but Crocker (not wanting to run into Crazy the Eighth Dwarf) spins it again and it lands on fairies, making everything go back to normal.