The Smith household on Christmas was shrouded in Jerry’s "Traditional Family Manifesto" — he’d confiscated everyone’s electronic devices, vowing to create a holiday atmosphere free from screen distractions, with the core goal of welcoming his visiting parents. However, this carefully crafted warmth was soon shattered by the sudden arrival of Grandpa Rick. Bursting through the door with a homeless man dressed as Santa Claus, Rick casually introduced him as Ruben before dragging him straight to the garage, leaving the family stunned in silence.
Jerry’s parents arrived as scheduled, but the young Black man Jacob who accompanied them completely upended Jerry’s understanding of "family." At first, Jerry assumed Jacob was a caregiver his parents had hired, feeling relieved that his mother would be well taken care of. It wasn’t until he accidentally caught Jacob being intimate with his mother that he learned the truth from his father’s nonchalant explanation: Jacob was his mother’s lover, and his father not only accepted it fully but the three maintained an absurd "threesome" relationship. The shock plunged the tradition-obsessed Jerry into extreme anxiety and resistance. Clutching the confiscated devices, he watched as his family seemed to take this bizarre dynamic in stride, his inner turmoil threatening to spill over. Meanwhile, Summer was frustrated by her boyfriend Ethan’s relentless flood of texts, and their argument was unexpectedly diffused by Jacob — this seemingly intrusive "family member" displayed an extraordinary capacity for empathy, guiding Ethan to voice the root of his anger.
The secret in the garage was far more bizarre than Jerry’s family drama. Rick pulled Morty over to Ruben and revealed his "side hustle": he’d built a miniature theme park inside the homeless man’s body — "Anatomy Park," transforming Ruben’s organs into wildly different attractions: the Cerebral Cortex Carousel whisked riders through a jungle of neurons, Colon Rapids offered a grossly thrilling rafting experience, Lung Launch simulated weightlessness with each breath, and there was even the "Pancreatic Pirates" themed area centered around the pancreas. At that moment, Ruben had fallen into a coma, and the park’s safety systems were on the brink of collapse. Rick insisted Morty shrink down and enter Ruben’s body to assist Dr. Bloom, the park’s manager, in troubleshooting the crisis. Before Morty could react, a shrinking beam hit him, and he was promptly injected into Ruben’s chest via a syringe.
Inside the human body, Morty soon met Dr. Bloom and park employee Annie. The blonde girl was initially wary of the impulsive intruder, but as they worked together, she gradually developed a fondness for him. Dr. Bloom led them through the organs, the scenery both spectacular and terrifying — the heartbeat thundered like a giant drum, and the blood vessel walls were crawling with out-of-control bacteria. Just as they detected an abnormality in the immune system, Poncho, a member of their team, suddenly revealed his true colors: harboring an old grudge against Bloom, he’d deliberately sabotaged the park’s safety barriers, allowing pathogens like Yersinia pestis (plague bacteria) and hepatitis A to run rampant inside Ruben. In the chaos, Poncho tried to kidnap Annie. Morty mustered up his courage and lunged to stop him. During the scuffle, Poncho was bitten by the plague bacteria, stumbled into the abyss below "Bladder Falls," and died instantly. Another teammate, Roger, had his foot stuck in intestinal mucus and ultimately drowned in excrement, leaving only Morty, Annie, and Bloom from the original rescue team.
Worse news followed: Rick monitored from outside that Ruben’s heart had stopped completely — the "living vessel" housing Anatomy Park was dead. As Ruben’s body began to decompose, the organ attractions collapsed one after another. Dr. Bloom decided to activate the "Skeletal Railway System," or the "Bone Train" as he called it, to escape through Ruben’s nipple with the two. To start the train, Bloom volunteered to stay behind and operate the switch. Just as Morty and Annie thought he was about to stage a heroic sacrifice, they heard his wails over the comms — he’d just discovered the train actually had autopilot, but by then his body was swarmed by E. coli and ultimately devoured. The train raced through the bones when hepatitis A viruses suddenly attacked from the side. Just as Morty and Annie thought they were doomed, hepatitis B viruses unexpectedly appeared. The instinctual enmity between the two pathogens made the former turn on the latter, allowing the pair to escape unscathed.
Outside, Rick was already prepared. He loaded Ruben’s body onto his spaceship, launched it into space, and activated a growth beam to restore it to giant size — this "naked airborne Santa" instantly sparked nationwide panic. When Morty and Annie reached the nipple exit aboard the Bone Train, Rick pressed the detonator he’d planted inside Ruben earlier. With a deafening explosion, Ruben’s body blew up in the sky, and fragments of flesh and bone fell like a red rain onto the Smiths’ roof. Inside the living room, the Jerry family, still troubled by their dysfunctional relationships, stared in silence at the bizarre "snowflakes" falling outside the window. The phones Jerry had confiscated became a mad scramble as everyone sought refuge in them, and no one mentioned a "traditional Christmas" ever again.
