Late at night in the Smith household, high school student Morty is indulging in fantasies about his classmate Jessica when his drunk grandfather Rick suddenly bursts through the door. Reeking of alcohol, he grabs Morty and announces he’s about to give him the "surprise of a lifetime." Before Morty can react, he’s dragged onto a shabby spaceship that hurtles into the night sky under Rick’s intoxicated piloting. As the ship lurches violently, Rick finally reveals the "surprise"—he’s built a neutrino bomb to blow up Earth and restart the world, leaving only Morty and Jessica as the "Adam and Eve of the new world."
Though tempted by the invitation to be with his crush, Morty’s reason ultimately triumphs over impulse. He lunges for the ship’s controls, and in the heated struggle, forces Rick to make an emergency landing in the desert. While Morty is still recovering from the shock, Rick collapses onto a pile of empty bottles and casually says it was just a test of his humanity before promptly falling asleep. This absurd late-night adventure sets the stage for family conflicts the next day.
At the breakfast table the next morning, the sleep-deprived Morty dozes off right on his plate. His sister Summer immediately exposes the truth—he’d "been fooling around with Grandpa all night." Father Jerry erupts in anger, accusing Rick’s reckless behavior of severely disrupting Morty’s studies and dismissing his father-in-law (who’d suddenly reappeared after years away) as a danger to the family. Mother Beth is torn between her husband and father, worrying about her son’s future while harboring complex feelings for the father she hadn’t seen in so long. Rick scoffs at Jerry’s complaints, mocking school education as a "collective farce that wastes life," before slamming the door and leaving the family to argue among themselves.
In math class, Morty—still distracted by thoughts of Jessica—dozes off again during a pop quiz. His romantic daydream causes a scene in class, earning him a public scolding from the teacher. After class, school bully Frank corners Morty to pick a fight, but Rick suddenly appears, freezes Frank solid with a cryogenic gun, and pulls Morty toward the school alleyway. "Don’t worry, he’s just temporarily turned into an ice sculpture masterpiece," Rick says as he opens a glowing green portal and yanks the bewildered Morty into another dimension.
In this dimension, canyon valleys are lined with "giant tree seeds"—contraband mystical seeds crucial to Rick’s experiments. Rick hands Morty a pair of special shoes that can adhere to any surface, but before he can finish explaining how they work, Morty—eager to prove himself—slips and plummets off a cliff, breaking both legs. Rick shrugs helplessly, opens another portal, and retrieves a healing serum from a dimension with advanced medical technology, healing Morty’s legs in seconds.
Just as the two are about to return with the seeds, they discover the portal gun has run out of energy from repeated interdimensional jumps. Rick comes up with a terrible plan—sneak back to Earth through interdimensional customs, but they’ll have to hide the contraband seeds in a "place no one will ever check." After coaxing and deceiving Morty, Rick convinces him to swallow the seeds to hide them inside his body. Morty, humiliated, follows his grandfather toward the customs checkpoint. However, just as customs activates a new internal scanning device, Rick grabs Morty and they run for their lives.
Chaos erupts in the customs hall as gunfire breaks out. Rick tells Morty to cover him with a gun while he inputs the Earth coordinates, lying that "these pursuers are all robots—shooting them isn’t a crime." When the portal finally opens, the two tumble directly into Morty’s school cafeteria, right as Jerry and Beth are meeting with the principal. Jessica glances curiously at Morty as he stumbles out of the glowing portal, making him instantly forget the danger—until Rick urges him to "get rid of the seeds inside you" and snaps him back to reality.
Back home, Jerry and Beth make up their minds to send Rick to a nursing home. "He’s only let Morty attend seven hours of school in two months, and he froze the school bully!" Jerry exclaims angrily. Though reluctant, Beth Jerry’s decision when she sees Morty’s chaotic school records. Just then, Rick suddenly suggests "testing Morty’s IQ" and fires off several advanced physics questions—much to everyone’s shock, Morty answers fluently.
Jerry and Beth fall into stunned silence as Rick smugly slings an arm around Morty: "He just needed the right guidance." Once their parents leave, Morty excitedly asks why he’s suddenly so smart. Rick takes a sip from his wine bottle and casually reveals the truth: "The giant tree seeds dissolved inside you. A side effect is temporary IQ enhancement—though you might be paralyzed for the next 72 hours."
As night falls again, Morty lies paralyzed on the couch, enduring the seed’s side effects while Rick assembles a new experimental device nearby. The night sky outside remains calm, but for the Smith family, with the arrival of this mad scientist grandfather, countless bizarre interdimensional adventures have only just begun.