Nick, a seemingly gallant boy, becomes a potential love interest for Lisa.
Marge and Lisa's mother-daughter Valentine's Day plans take a turn when Lisa meets Nick (guest star Michael Cera), an intellectual romantic who shares the same passion for culture, history and literature.
The episode opens up with a shot of a Valentine's Day card and a letter, then pans to a large pile. Bart and Milhouse discuss their valentines; Milhouse got one from Lisa and one from his optometrist, who Bart says merely sent him a bill, with Milhouse saying it's a valentine due to the heart stamp. The two then watch TV, a valentine "Itchy & Scratchy". Milhouse's father appears at the window to tell Milhouse not to watch, as it gives him night terrors, but is rebutted by Milhouse, who says that he had the night terrors last night. The two then switch to Mythcrackers, a parody of Mythbusters. Marge comes in and tells them not to watch TV, telling them to play outside as it's a beautiful day, prompting the two to switch to watching it on a computer then a smart phone, each time stopped by Marge, finally getting to watch it at a gas station, causing a long line of cars to start honking their horns.
The Mythcrackers try to prove or disprove the myth that a cat always lands on its feet, performing an ill conceived experiment to try and prove it, involving a build a bear, a steam cannon, and making a graph of the remains. Milhouse says they should become mythcrackers, saying it would make them cool. Bart is unsure, as it was Milhouse's idea, but says ok anyway. Milhouse tests their first myth; whether using a cell phone at a gas station is dangerous, taking out his cell phone, which sparks immediately, causing him to throw it and cause an explosion; a large "CONFIRMED" stamp appears on the screen. Milhouse then says that he's at least cool now, making a large "BUSTED" stamp to appear.
The scene then cuts to Homer as he prepares for Valentine's Day, taking a bite out of a rose to help freshen his breath. Bart shows up and asks why men have to do everything for women on Valentine's Day, with Homer saying the reason is because they let the men blow up things on July 4th, saying he hopes they will never fall on the same day. Marge comes in an gives Homer her Valentine, reading it aloud for him as he reads it. Marge tells him to have the day to himself, saying they should show their love every day of the year. Homer tried to still celebrate it, but is convinced by Marge to go out with Bart. The two go to Testoster-Zone, a baseball place where they go to the batting circle. Homer taunts a passerby, who calls him a "lucky bastard", since he doesn't have to spend the day with his wife, who is in the car with him, and says he was talking to his own reflection in the mirror. The man yells that he hopes Homer hits his hands on a ball, and he does. Homer is then shown playing several games with Bart.
The next scene shows Marge and Lisa in a restaurant, where Marge tries to connect with Lisa. Marge sees someone about to dip a ladle from one serving into another, and goes to clean it up. Lisa then looks through a crack, seeing a boy reading a book. She says sorry, but the boy talks to her, saying romantic things to her. They meet at the dessert table, where the boy, Nick, throws a fork into the air, saying he'll eat what ever the fork lands on. Lisa tires to tell him her name, but is stopped, saying he wants the first place he hears her name to be special, but Lisa says it anyway, saying the place they were was now the most special place. Marge sees Moe through the crack, who offers her a piece of his ziti, who takes it. Moe then says that she owes him five cents for the food, but that they'll talk about it later.
The next day Lisa meets Nick again and focuses on him as all around her bad things are happening (such as Gil bathing in the water fountain and Snake throwing a tied up and gagged Apu in a dumpster). The relationship goes so well until Marge grows jealous that Lisa is spending so much time with Nick. In order to be sure Nick is the right person for her, Lisa consults Abe's advice, who then tells her that their relationship resembles the same one from a story book (which is quickly labeled as a Disney version inside Lisa's imagination due to adding a talking parrot to it) and that they must kiss under a tree to seal the deal for eternity. Convinced that she and Nick must kiss under a tree on a small island, Lisa takes Nick with Grandpa's help, while Marge and the others chase after them to stop the kiss. Arriving at the island with the tree, Lisa receives an epiphany and, coupled with Nick's rather insecure behavior showing up since they (or rather Lisa) rowed a boat, starts to doubt kissing him. Once Marge manages to reach the island, Nick reveals to Lisa they can't be together and admits "God gave [him] a gift to lie to ladies" and departs, leaving Lisa and Marge alone, where they both kiss each other to fulfill the eternal love for one another under the tree.