Rick, in a drunken state, takes his grandson, Morty, for a ride in his flying car and rambles on about how he plans to use a neutrino bomb to wipe out all life on Earth. Rick lands the vehicle on Morty's demand and passes out. The bomb activates by itself and seems to be left unchecked, but ultimately it is shown that life on Earth remains intact. After having breakfast with their family, Rick takes Morty to another dimension to collect seeds of "Mega Trees", which Morty is forced to hide in his own rectum to get past intergalactic customs. However, Rick and Morty's cover is blown and they escape while engaging in a shootout with alien insects. Ultimately, the seeds briefly cause Morty to be highly intelligent, despite the fact that he missed a semester of school because he's been in adventures with Rick. This causes his parents to believe he is fine with his education, but this wastes the seeds, so Rick informs Morty that they need to go back and get more, while their aftereffects leave Morty writhing on the floor.
Morty is interested in going to the dance at his school with his classmate Jessica, so he asks Rick for a love potion. However, because Jessica has the flu, the potion becomes airborne and goes haywire, causing not only her but the whole population of Earth to fall for Morty save for blood relatives. Rick attempts to fix up an antidote, but he fails twice, ultimately causing all humans affected by the love potion to turn into mutated monsters called "Cronenbergs" (a reference to famous director of body horror films David Cronenberg). Meanwhile, Jerry visits Beth in her workplace because he is concerned about her fidelity, and they find Summer later. Rick and Morty then migrate to another dimension where their duplicates died soon after successfully curing all of Earth, thus allowing Rick and Morty to assume their roles.
Post-credit scene: Jerry, Beth and Summer are happy to stay together as the only normal human family in their post-apocalyptic mutated world, glad that Rick and Morty are gone. Two Cronenberg versions of Rick and Morty come from the "Cronenberg world" to live there as well, because their home was inhabited by Cronenbergs all along, which were accidentally transformed into normal people.
As the family watches The Bachelor, Rick is dissatisfied with the quality of Earth TV so he upgrades the cable to show programming from every conceivable dimension. Eventually, they see Jerry from an alternative reality on TV. The family, minus Rick and Morty, uses Rick's goggles to see through the eyes of their duplicates in that alternative reality, where Jerry and Beth have successful lives, they never married, and Summer was never born because Beth had an abortion. Jerry, Beth and Summer have a heated discussion in which they conclude that family life is holding them back and Beth admits that Summer was an unwanted pregnancy. Summer feels unwanted and plans to run away, but Morty tells her that he and Rick themselves came from an alternate dimension (as depicted in "Rick Potion #9") and persuades her to stay. Ultimately, Beth and Jerry discover that their alternate selves are miserable in their own ways and witness them getting back together, which convinces them that they belong together too.
Post-credit scene: The family goes on vacation into an alternate reality where hamsters live in human rectums that they saw on the interdimensional TV.