While the family is eating breakfast, Rick kills an alien parasite who was posing as Jerry’s brother Uncle Steve. Rick then warns the family that they might be infested with alien parasites, which are capable of creating and manipulating memories to convince their hosts that they have always been longtime acquaintances. To prevent the spread of the parasites, Rick locks down the entire house, behind security shutters. More and more parasites appear as different zany characters introduced during flashbacks (including but not limited to Sleepy Gary, the family butler Mr. Beauregard, Frankenstein’s Monster, Pencilvester, Tinkles the Fairy Lamb, and the Reverse Giraffe) and try to convince Rick and the family to lift the lock-down. The parasites also begin sowing mistrust among the family that they
might be the parasites. Most of the family is quickly swayed by the parasites, while Rick begins to question his own sense of reality. Finally, on his way to execute Rick as a believed parasite, Morty comes to the realization that while the parasites can manipulate memories, they can only create positive
memories. The family is then able to confirm each other’s existence, due to the various negative memories they have of each other, and begins killing all of the parasites of whom they are unable to recall negative memories. After which they have dinner and Beth, still believing him to be a parasite, shoots Mr. Poopy Butthole who is revealed to have been a real friend all along. Beth sneaks away, devastated by her mistake, and begins drinking.
Post-Credit Scene: It is revealed that Mr. Poopy Butthole survived the incident and is going through physical therapy when he turns away the visiting family, because he doesn’t want to see them. He tells his physical therapist to apologize on his behalf for the family having no bad memories of him. Beth is still devastated at her mistake as Rick comforts her. Rick then closes out the scene with one of his catchphrases.