Catch 'Em if You Can is the eighteenth episode of Season 15.
When Bart and Lisa realize that Marge and Homer have gone to Miami for a second Honeymoon (instead for the birthday of their uncle), the kids do what they can to ruin their parents' second honeymoon.
Bart lectures other students on the school bus about water balloons, and to demonstrate, he throws one at Lisa. Lisa and Bart then fight on the bus all the way home, and fighting in the house, Marge stops them, and tells them that they are going to Dayton, Ohio (and staying in the Dayton Arms Hotel) to celebrate their Uncle Tyrone's birthday. However, Bart and Lisa aren't thrilled with the idea, and they are going to stay home with Grampa. As a family activity, the family rents the film Love Story, and as Bart and Lisa are bored with the movie, they ruin any special moment that Homer and Marge could have had watching the film. Homer and Marge then look forward to their trip without the kids. However, at the airport, they see a line for a trip to Miami, and after thinking it over, Homer and Marge agree that they will not go to Uncle Tyrone's birthday celebration, and instead go to Miami as a second honeymoon.
In Springfield, Bart and Lisa watch television with Grampa and learn that a tornado is wiping out the Dayton Arms Hotel that Marge and Homer were supposed to be staying in. However, a little bit later, they get a call from Marge, whom says that all is well. Growing more suspicious, Bart uses last-call return to find out the last incoming phone number, and the pair learn that their parents are instead in Miami. After persuasion that many single beautiful pensioners will be there, Bart and Lisa get Grampa to take them to Miami. Returning to their hotel room, Marge and Homer see Bart and Lisa sleeping in front of the door. After choosing to not let their kids ruin their fun, Marge and Homer run off again.
Homer and Marge this time run away to Atlantic City, where they see the children on their trail once more. Homer and Marge go on the run again in a musical montage and an animated sequence. Homer and Marge then find themselves in Niagara Falls, but the kids are there as well. Bart and Lisa confront their parents, and Homer and Marge say they just wanted some time to themselves but the kids smugly say that they have kids so those days are over. The two give in and allow the children to stay with them. That night, Bart and Lisa feel guilty for ruining their parents' good time, and plan to go to an amusement park, but find that their parents sneak out and went to that very amusement park. Annoyed, thinking their children are on their tail again and refusing to allow them to explain, Homer and Marge hide in an inflatable castle (which is being repaired). Homer and Marge start to have sexual intercourse, and all the bouncing around causes the castle to go over the Niagara Falls. After Canadian and American rescue teams fight over who gets to rescue them, Homer and Marge's inflatable castle goes over the falls, but they are saved, as the castle doubles as a flotation device. When the rescue teams ask them if they need help, a naked Homer and Marge yell that they do not need any help, and they continue having sex underneath the Falls.
Back in Springfield, Ned and Rod are horrified to see their credit bills which Homer and Bart raked up with the cards they stole from them.