Fed up with yet another argument between the Smith couple, Rick dumps Beth and Jerry onto Nuptia 4, an alien marriage counseling institution with the highest success rate in the known universe. Counselor Glexo Slim Slom leads the Smiths to a machine designed to create a biological artificial representation of their respective partner's true feelings for each other. Jerry sees his wife as a domineering egomaniac, so he subconsciously creates a monstrous scorpion-like creature of Beth. Angered, Beth envisions her husband as a pathetic coward, thus she conjures up a whimpering worm version of himself.
The representations—known as Mythologs—are placed in cells for Beth and Jerry to gawk at. This is to help them gain perspective on their marriage because unlike them, monsters cannot be reasoned with. Glexo severely underestimated the minds of Beth and Jerry though. Monster Beth realizes her squiggly husband can stretch his body to limitless proportions. Using that ability, she outsmarts the Nuptia guards and make her escape. The Mythologs have done the impossible, they've become codependent.
Monster Beth reigns chaos until she kidnaps her real counterpart and places her back in the machine to create more Worm Jerrys. She sees the potential in using Jerry as her subservient and creates an army of them so she can rule the universe. Beth quickly points out a huge flaw: instead of creating Jerrys, she could amass a legion of herself instead. Monster Beth dismiss her, saying there could only be one of her because Jerry thinks so highly of Beth (to his own detriment) that she ended up as the smartest creature alive; adding another would only invite further complication.
Jerry has spent much of the rampage hiding while his wife does all the work to find a way out. He is eventually chased off by his counterpart until he's backed into a corner. Jerry tries to put up a fight, but Worm Jerry reacts submissively. Annoyed that this is how Beth sees him, Jerry finally gains the courage to rescue his wife. He plows through the army of Worm Jerrys, impressing Beth enough to start creating handsome, well-muscled Jerrys. They, too lend their hands in battle (though when Jerry gets a bit prideful, she also envisions self-congratulatory Jerrys that do nothing but praise themselves.) The battle is ultimately won when Jerry places the helmet on one of the Handsome Jerrys. He conjures a Goddess Beth who quickly defeats Monster Beth. Jerry figured if he sees Beth as a smart, powerful figure, then his better self would see her for what she is: a Goddess.
Nuptia 4 was a bust, but it did force Beth and Jerry to realize they can hold off any permanent issues until Morty graduates from college. After that, all bets are off.