The Simpsons are invited to Milhouse's birthday party, which is shown to be a big expensive party, so much that Kirk has to sell the house in order to pay for it. When Marge and Homer think that all birthdays are getting too expensive, Homer takes drastic measures by ruining other kids' big birthdays; however, the party committee discover Homer's deeds and at first put a black mark on the Simpsons, preventing Bart, Lisa and Maggie from ever having another birthday party, but Homer is given a deal to make sure the kids can have one again. Homer must give Rod a magical birthday party or the black mark will remain (that and Bart threatens to wake Homer up on Saturdays with pots and pans). When the party takes place at the Springfield Air & Space Museum, the Simpsons are surprised when one of the veteran pilots being honored at a ceremony recognizes Grandpa and tells them of Homer's dad's service with the pre-USAF air command services during World War II. The veterans aren't happy that Homer and Grandpa are estranged and actively intervene in the relationship, forcing Homer to hug Abraham at gunpoint. Grandpa eventually reveals that he was in love with a waitress at the main diner near the base but wasn't brave enough to attract her attention, so he stopped his regular maintenance job and took a supersonic flight that nearly killed him but won over the waitress—who was Mona, Homer's mom.
Bart undertakes his own quest to get a girl to like him when Milhouse's Dutch cousin Annika shows up for a visit. She constantly complains about American culture and introduces Bart to goofy Dutch games and vaping, which he gets addicted to. When Annika is heading to the airport to fly home, Bart desperately races there so he can talk to her before she goes. Annika scoffs at his typical "American gesture" but Bart shuts her up by telling her he actually doesn't like her because she does nothing but complain and is only nice to people when she wants something from them. He dumps the remaining e-cigarettes and walks away from her, leaving Annika feeling humiliated by being dumped by a friend of Milhouse's and starts cursing in Dutch. Homer and Grandpa are on good terms again and Homer first grills, then blends up, a big steak to honor his heroic dad. When they don't work, he puts it in an e-cig, to Grandpa's pleasure.