Doug and Carrie Heffernan are a couple whose castle is invaded by Doug's father-in-law, who comes to live with them.

Doug is afraid he'll lose Carrie when her boss drives her home in his Jaguar and gives her tickets to see a famous cellist.

When Doug takes Carrie's dad out for the night, Carrie shows her appreciation in a very amorous way, which leads Doug to spend more time with Arthur.

For Christmas, Arthur surprises Doug and Carrie with a new car--an appalling compact made in Luxembourg.

Arthur hits it off with a woman at a Valentine's Day dance for seniors.

Doug and Carrie feel pressure to have a baby after learning that a friend is pregnant. Meanwhile, Arthur recalls when Carrie was born.

Doug becomes a Big Brother. Which leads him to running a 10K race to support heart disease; Carrie accidentally tells another Doug she loves him.

Carrie discovers that she is pregnant and she is panicked that the timing is all-wrong. Meanwhile, Deacon and Kelly begin to reconcile and Spence is left out in the cold and Arthur insists that Doug build him his own bathroom in the basement.

Doug tells Carrie not to panic about having the baby, that he will take care of all her "burden," so he takes on a second job so that they can store a little extra money before the due date. Meanwhile, Arthur is annoyed that Doug still hasn't finished his bathroom and Deacon and Kelly reconcile.

The Heffernans are again thinking about getting pregnant, just four months after Carrie's miscarriage. But there's one problem: Arthur. Now that his last friend from the senior center has moved away, Arthur naps all day. By the time Doug and Carrie get home, Arthur is full of energy and has no one but them to unleash it on. Quality time alone for the couple is impossible. That is, until Doug hires an attractive dog walker to occupy an unsuspecting Arthur: she takes him for a stroll three times a week, under the guise that she's a student interested in learning about his World War II experiences

As Doug is about to break what was once thought of as an unbeatable record, the tension between he and the guys at IPS mounts. For 18 years, Iggy Stenkowski's record of 951 consecutive perfect delivery days has remained intact, and the guys resent Doug as he's about to beat it and replace the legendary Iggy's plaque with one of his own. As he deals with his internal conflict, Carrie has trouble dealing with the fact that Holly, the dog walker, actually enjoys spending time with Arthur. She starts to wonder if her father really is as great as Holly thinks he is and that maybe she's the problem in their relationship.

Doug and Carrie get free tickets to her firm's annual golf outing at a private club. They have four tickets and usually bring Deacon and Kelly, but with their recent separation, things have changed. Not wanting to lose out on the opportunity, Deacon meets an available gal, Leslie, who he brings along to complete the foursome. Doug and Deacon are having a great time, but unfortunately, Carrie is not feeling the connection with Leslie and makes an attempt to set Deacon up with another co-worker while at the golf course that she thinks she'd have a better time with. In the meantime, Deacon asks Holly to watch his kids over the weekend while he's gone but doesn't realize that Holly may be pining away for him.

The fourth season concludes with Arthur visiting a psychiatrist and recalling via flashback a disturbing encounter with his dad that may explain Arthur's abrasive personality.

Doug's bowling team prepares for a tournament, while Carrie agrees to babysit Mr. Kaplan's son, in hopes of furthering her career. But when Doug throws out a mercy flirt and Carrie runs into an awkward set of hands, all goes downhill.

Carrie thinks Doug needs professional help to control his excessive eating habits, so she persuades him to see a therapist. When Carrie sees Doug's great inprovements, she asks the therapist to work on Doug's other issues. Meanwhile, Arthur believes he's addicted to nasal spray and fights to stay off of it.

The mold problem in the Heffernan household grows and Doug and Carrie find out to fix the problem will cost them $12,000! Doug, with his tail between his legs, goes to his father to ask for the money, but hits a wall when he wants to know why he and Carrie don't have it in the bank. When Doug has to admit they have no savings, his dad wants to comb through their financial books to see where all the money is going. This prompts Doug to limit Carrie on her "wild spending," which does not go over well with her.

When Doug hears from Carrie that Deacon's ex-wife wants to reunite with him after a two-year separation, he can't decide whether or not to give Deacon the heads-up. When Deacon informs Doug that he just met a beautiful stewardess and is spending the entire weekend with her, Doug decides not to tell him about his ex-wife's plans to reunite with him. But when Carrie discovers this, she demands that Doug tell Deacon so he doesn't ruin his chances of getting back with Kelly.

It's Thanksgiving in the Heffernan household and while Carrie cooks dinner for ten people, Doug lets a stranger into the house to use the phone. He is convinced the stranger is a nice guy but Carrie is not so trusting. Everyone at dinner feels sorry for the man, who's been left outside to wait for a ride, but when Carrie finally gives into the holiday spirit, it turns out her instincts may have been right.

Doug must heal the breach between father and daughter when Arthur ruins Carrie's job interview at a prestigious real-estate development firm by making a nuisance of himself in the company's lobby.

When Doug wins a trip to St. Louis to see the Final Four, he is reluctant to bring Arthur. However, Carrie tells him that if he does this, he never has to take him to the senior center or see his naked back again. However, the plane gets delayed & Doug & Arthur go to Pittsburgh. Then, things go downhill with Doug missing the Final Four by being stuck in Dayton.

Doug convinces Carrie to take pole dancing lessons, but is disappointed when she puts on a show for him. Meanwhile, Arthur worries her new hobby is a result of his poor parenting, and smothers her in effort to make up lost time.

Doug and Carrie's marital tension continues, as they ponder whether they have a future together. Arthur and Ava's wedding day turns problematic.

At Arthur's wedding reception, Doug and Carrie's marital tension continues, and they ponder whether they have a future together.