"Adventures in Baby-Getting" is the third episode of Season 24.
When Marge's car falls into a sinkhole, she has a problem with her new one - it won't fit the entire family if they include the baby she wants, and Bart tries to figure out why Lisa has written bizarre messages and is sneaking into town after school.
After Homer fails to fix a leak in the hose faucet, the ground under Springfield collapses from mass of water and causes a sinkhole in the middle of the city. Marge, Lisa, and Bart are driving and Marge's car falls through the sinkhole as the ground collapses and ruins her car. They get back to the surface using Marge's Sinkhole Kit. The city finally covers the hole with the Springfield Tire Fire and it solves the problems and difficulties for everyone. But Marge's car is still down there and then gets crushed.
Meanwhile, at school, Bart and Milhouse discover that Lisa skips the bus ride home. The boys see her take a taxi, dropping a piece of notebook paper. They catch it and it reads, "The five boxing wizards jump quickly" in cursive. Bart gets more curious and tries to find a clue in Lisa's room. He gets Nelson, Principal Skinner, and Ralph involved with figuring out Lisa's messages, who leaves another one saying, "Sphinx of black quartz, judge my vow." Skinner finds out that Lisa is going after school to a friend of his to learn cursive, because they don't teach it at Springfield Elementary.
Meanwhile, Marge and Homer go looking for a new car in the dealership and Marge buys a snazzy red car. But fitting in it is difficult and Marge is uncomfortable and frustrated. One night, when Homer and Marge return home, Homer suspects she may be stressed because the car and her don't get along. Marge then says she feels like she wants another baby and she is under peer pressure because the car can't even suit three children, let alone four. But they find out Homer's sperm is dead and they go to Moe's Tavern and get advice from Lenny, Carl, and Moe to get some saved sperm Homer left at the sperm bank.
Homer does not want a fourth child and he stalls Marge as much as possible. After spending all day in the Christmas Ornament Museum, they separate after sex at a motel when Homer confesses he does not agree with Marge's plan. The next morning, they go to the sperm bank and Homer agrees he will do anything that makes her happy. He rescues his last sperm pack from a young couple planning to use it but Marge discovers that on the billboard of babies, a lot look like Homer. After the doctor places up a photo of sextuplets that look like Homer, Marge says "Maybe we'll wait" and the couple agree that three is good for now. As the episode finishes, Homer observes the sextuplets he saw in the photo pull up in a car beside him. They all exclaim "D'oh".