While in a field, Lisa finds an extract in a desert flower known as Silvertongue that has the ability to calm desert animals. When it's applied to humans, mainly seniors, it calms them as well to the point a saleman wants to make a version for the public. That is until an 'eye-popping' problem is known.
While on a field trip to Satan's Anvil, a desert region surrounding Springfield, Lisa falls into a scorpion pit whilst studying the dangers of the desert and then finds that when her scorpion tormentors set foot in a flower named Silvertongue the effects of the flower eradicates their aggression. Lisa soon extracts water from the plant and found out the reason for the Silvertongue effects on desert life. Lisa brings the scorpions and a clipping of Slivertongue home to conduct further research. However, problems strike: Abe, their Grampa, is thrown out of the Springfield Retirement Castle after insulting one of the staff. He has to live somewhere else - With the Simpsons, as Bart predicts. Grampa, while having dinner (sour crème and chives), complains having food made from the regular century, claiming he preferred having woodchips and barber hair, forcing the family to take turns of who Grampa has to sleep with. Homer attempts to have Maggie sleep with Grampa "forever and ever", but Maggie literally shuts him up by placing her hairbow pin over his lips. Bart ultimately has to sleep with Grampa first. Grampa then calls Bart rude for reading a comic book and not talking to him. Bart attempts to ask Grampa how its going, but Grampa says its terrible, and insults Bart by saying that he has a roommate who won't stop yapping. The next night, its Lisa's turn to have Grampa sleep with her, with Grampa crudely implying that Lisa won't get a man with her brains, regardless of her looks. The night after that, Homer and Marge are stuck with Grampa, and Grampa wakes up to witness them making love (a fact that Marge apparently warned Homer about, but Homer brushed off), and criticized their attempts, and also talks back to Marge by stating that back in his day, women were silent.
During her research, Lisa shows Homer her work. Grampa is behaving in a rude and irritated manner and therefore Homer concludes that if the flower has the effect of making hostile scorpions docile, then the flower must make angry Grampa's docile. He sprays some of the Silvertongue's water in Grampa's coffee and the following morning he has becoming increasingly optimistic, more so than usual. The effects of the Silvertongue water are so astonishing and unique that a German doctor soon finds out about this unique effect and, after testing the water on Grampa, extracts the right solution and duplicates it using beautiful German women as experiments. The doctor warns the Simpsons that if the solution fell into the wrong hands it would get into the black market and thus cause major damage to his reputation. Inevitably Bart seizes the opportunity to make money and sells the drug to miserly old citizens of Springfield, including Agnes Skinner, Mr Burns, and numerous residents of the Retirement Castle.
The solution appears to have indeed increased the optimism of the elderly, until Grampa's eyes pop right out of his face when he is telling Lisa how good he feels about his life. Lisa and the Simpsons are shocked at how such a good drug could have such a bad effect, and Lisa sees the scorpions from Satan's Anvil have their eyes popped out of their head as well. Marge is initially relived that only Grampa has had the Silvertongue solution, until Bart admits he has sold the drug to numerous residents of the town, causing an outbreak of blind people, most of them elderly.
The old blind people converge together to form what initially seems to be an angry mob, but then Grampa explains to them that the biggest mistake they made was letting Homer's generation get away with doing nothing with all the products of his generation's hard work. Grampa and the elderly blind citizens push their eyeballs back in, restoring their vision, and set about giving Homer and his generation something to live for, as opposed to the mob-like attitude they had earlier. Or as Homer puts it, the last generation's "can do" attitude balances out his generation's "won't try" attitude.