Greg and Kim live in their own home in California. Christine (Kim's sister) and Jimmy live in a nearby apartment. Jimmy talks Greg into allowing Kim and Christine to have a day without the children; he and Greg take the children. to a casino.
The two couples take their children to the park. Greg and Kim meet a young couple with a child and think they will be a fun couple to know; Christine and Jimmy meet an older couple with a child and Jimmy is chagrined to be with older people.
While Kim and Christine go to the theater, Greg and Jimmy go to a sports event and then stop off at a strip club. That evening, Greg and Kim have adventurous relations; Kim is pleased until she finds out why Greg was so enamored.
Kim and Christine's father comes to visit. The father gets along great with Jimmy, but not with Greg. Jimmy can get away with saying anything and the father does not get upset. With Greg, things don't always go well.
Greg's birthday is coming up, and Kim wants the family to go to Disney Land. Jimmy talks Greg into partying like when they were young. Greg and Jimmy go out, but partying is different when you are older.
Kim invites Christine to join her in a Mommy and Me class with their children. Kim's day is structured with the class, a walk, the park, and more. Christine is worn out. Kim and Christine argue over parenting styles.
When Kim finds out Christine and Jimmy are not having a birthday party for Dominic's birthday, she has one for him. Jimmy gets a security guard job where Greg works at the movie studio and invites the Greg's boss to the party.
Kim's father visits. When he sees the sleeve guards Kim created, he convinces her to sell at a craft fair. Jimmy plays on a security guard baseball team, and wants Christine and Dominic to watch the game.
Kim and Greg have dinner with friends. When they realize they only talk about Sammy, they decide to take a wine tasting class to have something else to talk about. Jimmy and Christine decide to join them in the class.
Jimmy inherits money from a deceased uncle. He repays Greg the money he owes him, and then spends the rest on gifts and other items. Now, he has no money to pay the taxes on the inheritance. Kim has a holiday picture taken of the children.
When an inspector shows up and tells them that Jimmy and Christine can't live with Greg and Kim cause of zoning. So they make plans to leave. The inspector tells Greg that if they can get their neighbors to sign an waiver, Jimmy and Christine can stay but he keeps it to himself. When Kim gets upset that Christine's leaving, Greg tells them about the waiver. So while the girls go the neighbors who are easy, Greg and Jimmy have to get Walt, a guy whom they avoid like the plague, to sign.
Billy, a friend of Jimmy's visits - with suitcase in hand. He stays in Kim and Greg's backyard. Billy makes himself at home, setting up clothes lines in the backyard, moving yard furniture, etc. Jimmy gets tickets for the hockey game.
The Warners and Hughes talk about the days when they first met and find out that Kim kissed Jimmy while he was starting to date Christine. Christine and Greg are upset. Greg claims to have kissed a lot of girls and Kim does not believe him.
Christine fears she is pregnant, and then is relieved to find out she is not. She wants Jimmy to get a vasectomy so they do not have any more children. Christine refuses sex until he has the operation.
Kim & Greg are upset to learn that Sammy's pediatrician has retired and sold his practice to another doctor. When they find out he is extremely young, they decide to find other choices. But then Sammy gets something stuck up his noise.
Greg is accidentally trapped into a family trip to Kim and Christine's parents. The mother does not like Jimmy and loves Greg. The house is too hot, the attention too intense, the requests over the top.
The two families decide to go to church with Kim having forced Greg to also go. Kim then tells him he has to go to the Daddies Group; Jimmy also has to go. They reluctantly attend until they find out what the group is really for.
Kim tells Christine she will watch her children if Christine accepts Jury Duty. Kim regrets it as she finds out what it is like to care for three young children. Greg calls Jimmy's mother to help Kim, but the mother is not that much help.
The couples get a baby sitter for the children and go out. But Kim does not have fun because they go to a bar for pool and karaoke. Greg implies Kim does not know how to be fun. Jimmy tries to help her learn how to have fun.
Kim talks Greg into allowing Jimmy's dog to move in with the family. Greg buys a go-cart to retaliate with Kim about the dog. Turns out the dog is not as fun loving at Jimmy remembers ... the dog is aggressive and no one likes the dog.
Greg & Kim buy a new car and plan to use their old mini-van for trade in. Jimmy repairs the van and sells it for more than trade in value. Greg lets him keep the extra above the trade value. Jimmy spends it on a shabby boat.