"The Old Man and the Key" is the thirteenth episode of Season 13.
In order to impress Zelda, a new female resident at the retirement castle, Grampa starts driving again, but Grampa runs into trouble with Homer whose car he continually abuses and he develops some enemies in the form of a rival gang of retirees at the Kwik-E-Mart.
The Simpsons receive word that Grampa has passed on. They rush to the retirement home, only to find out that Grampa is very much alive and healthy. It was another resident by the name of Stimson who actually passed on. A short time later, a beautiful new resident, Zelda, moves in. Grampa is instantly smitten, but it soon becomes apparent that Zelda is more interested in Zack, an elderly man with a minivan. Grampa concludes that if he wants to win Zelda, he must get his driver’s license back. At first, Homer is against the idea as it being too dangerous, but he eventually gives in and Grampa gets his license.
When Grampa asks Homer if he can borrow the car for a hot date, Homer refuses, but Marge dreams up the idea of a double-date at a drive-in movie theater. As the date gets underway, Grampa and Zelda make out in the back of the car. When Grampa makes off with Homer’s car so he can drive Zelda around, Homer puts his foot down and forbids Grampa from driving it. Later, at the Kwik-E-Mart, Grampa and his elderly friends are confronted by a group of elderly Hispanic gentlemen, who challenged them to a death race. Grampa and his buddies participate in the dangerous race and win…but crash Homer’s car into the back garden. Furious by his betrayal, Homer forbids his own father to drive ever again.
Grampa is crushed when Zelda accepts Zack’s offer to spend some time in Branson, Missouri. With help from Bart, he hot wires Marge's car and heads off to win back his love. Homer and Marge deduce where Grampa has taken the car. They choose to take a bus to Branson so they can confront him. Bart and Grampa follow Zelda and Zack into a Branson theater, where a huge musical revue is underway, featuring a huge cast of faded stars. Suddenly, Grampa stops the show. He tells the audience he drove hundreds of miles to say something special to someone in the audience. He then invites Zelda on stage, but when she draws close, and says “drive me,” Grampa tells her that their relationship is over. During the credits, The Simpsons wave in front of the studio.