Popular 15-year-old basketball playerKyle Johnson learns that his school is putting on a special event called Heritage Day, a celebration for everyone of different heritages. He asks his parents, but they're reluctant to tell him the truth about where their family came from, insisting they were from Cleveland, Ohio. After discussing his unknown heritage with his friend Bonnie Lopez, Kyle tries to research his family history, stumbling upon his father Bob 's high school yearbook, which lists him as "Robert Smith", leaving Kyle to wonder about what his parents might be hiding about his lineage. Over the weekend, Kyle and his best friend Russell Halloway attend an Irish carnival. Afterward, strange things happen: Kyle starts shrinking, his hair turns red, and his ears become pointed. His mother, Kate, starts speaking with an Irish accent, and confesses that their family is Irish. She changes her hairstyle, starts making Irish foods, and eventually shrinks to only a foot tall. His father is American and from Cleveland. Kyle then fails miserably at a basketball game, causing everyone in the school to turn on him, glaring and grumbling while praising another player named Drake. At school, during science class, Kyle realizes his lucky gold coin was stolen when the fake coin he was wearing stuck to a magnet he was using. It turned out that the gold coin Kyle wore was the O'Reilly lucky coin. A magic coin, when in the possession of the youngest family member, allows all the leprechauns in the family to pass as normal human beings. But since the coin is gone, the family is down on their luck now, and reverting to their true forms. At first, his mother believes that her 200-year-old father Reilly O'Reilly stole the coin, and they decide to go to his potato chip factory to get it back. Bob explains that his grandfather disowned his mother for marrying a human, and they not only left Cleveland, but also changed their original last name from Smith to Johnson so he would not be able to find them. After Kyle meets his grandfather, and explains what happened to the gold coin, he tells Kyle that it was a "far darrig", an evil leprechaun named Seamus McTiernen, who stole the coin. Seamus and his lackeys are given chase by the Johnsons, Bonnie and Russell in Bob's car, but manage to shake them off. After Bonnie and Reilly encourage Kyle not to give up, Kyle, Reilly and Russell set out to find Seamus and his followers at the end of a rainbow trailing to their whereabouts. While Seamus and his followers are busy in celebration, Kyle and Reilly sneak into Seamus' RV to get the gold coin back. Upon them finding it, Seamus senses that something is wrong. As Kyle regains his human form, Reilly's starts to change back only for Seamus to manifest as a tornado and capture Reilly. As Kyle starts to leave, Seamus appears outside, holding Reilly by his beard, while his followers have restrained Russell. Seamus demands that Kyle returns the coin, while Kyle states that the coin is his. Kyle challenges Seamus to a wager to see who gets the coin. Accompanied by Russell, Kyle is transported to Ireland to engage Seamus in several traditional Irish competitions, managing to tie in the final score. When Seamus uses trick wording to try and win, claiming their tie does not count as a win, Kyle makes one last bet with him to play a competition of his choosing as a tie breaker, to which Seamus accepts after Kyle offers to be Seamus' slave if Kyle loses. Kyle and Russell find themselves in a basketball game, with Seamus and his forces on the opposing team, commanding a strong lead thanks to the coin's luck. Russell gains confidence and improves when Kyle's grandfather gives him a fake magic lucky coin and tells him it's real, giving Kyle the realization he can make his own luck through hard work. Working together, Kyle and Russell catch the score back up, and shoot a winning shot, despite Seamus growing in power and showing his true form. Victorious after winning the bet, Kyle has Seamus shrunk and teleported to live within the shores of Lake Erie when Kyle states that his father is from Cleveland. At the Heritage Day event, Kyle performs an Irish folk dance and, with the help of Bonnie, leads the crowd in singing "This Land is Your Land", with his parents, his grandfather and Russell in the audience proudly joining in.
