After Holly gets kicked out of her apartment, Arthur insists that she stay with him in the basement until she finds a new place, making Doug realize the benefits of having two women in his life.

Doug and Deacon, who are out of work because of a strike, resort to playing sophomoric pranks, along with Arthur, to keep from going stir crazy. But they're driving Carrie and Kelly nuts. Eventually, Doug and Deacon return to work leaving Arthur alone.

Doug befriends a driver from one of IPS' competitors, but eventually discovers it's just a ruse to make him the butt of a joke. Meanwhile, Carrie becomes a mentor for a troubled teen, but isn't the best of influences.

Carrie, Doug and Arthur languish at a crowded market on the day before Thanksgiving, while Arthur shames Carrie into planning a huge feast.

When Carrie's new afterwork routine of apple martinis-along with an accompanying much more relaxed attitude-come to an abrupt end, Doug and Arthur join forces to keep her drunk, a course of action Lou doesn't approve of.

Doug, while goofing off at work, accidentally ends up with a staple wound to the scrotum.

Now that Arthur is back from the hospital, Carrie thinks that it is a good idea that she and Doug get life insurance. She wants to be sure that Arthur is well taken care of should something happen to either one of them. But this comes as a huge shock to Doug because he's never thought about having to take care of Arthur if Carrie weren't around. Once Doug finds out that Carrie has started smoking again, he's convinced that she's trying to die first so that he gets stuck with Arthur. They both lose sight of why they're signing the insurance forms and Arthur has to snap them back into reality. Meanwhile, Doug and Carrie have installed an Arthur cam so they can monitor him while he's down in the basement. Deacon, Spence, and Danny get a real kick out of watching Arthur's mundane daily activity and find themselves addicted to "Arthur TV".

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.

Carrie has been put in charge of overseeing a group of people who will be organizing and distributing legal documents for one of her firm's big cases. The catch is that her team will have to work the night shift, and they're "not the sharpest tools in the shed." Doug is disappointed by her new appointment because this means that they won't be spending any time together, but then decides to use her time away as an opportunity to do whatever he wants – eat in bed, not brush his teeth before he goes to sleep, etc. Unfortunately, he starts to get a little lonely but soon discovers that Arthur makes a suitable companion to keep him company.

After countless times of babysitting Deacon and Kelly's children, Doug and Carrie feel that Deacon and Kelly should return the favor and babysit Arthur every once in a while. Deacon and Kelly decide to take Arthur out to dinner so Doug and Carrie can be alone, but they ignore a warning about Arthur's reaction to spicy food.

Carrie gets jealous when Doug's attention is focused on Spence's new girlfriend, Becky, a professional chef. It's not her looks. It's not her personality, it's her food! Doug can't get enough and Becky comes to rely on Doug to sample all of her new recipes. Carrie, feeling left out, finally reaches the end of her rope and demands that Doug stop his "food affair" with Becky.

At a wedding, Doug takes a naughty picture with a disposable camera supplied by the bride and groom. After letting Danny take the blame, and after confessing to a priest, he has the dreaded task of coming forward with the truth.

A toy from their childhood leads to a rift between Deacon and Doug. Meanwhile, Carrie tries to give her father a great Christmas gift, but this proves hard to do when everyone thinks of the wrong gifts they are receiving, altering their original gift choices.

When the partners of Carrie's law firm notice Doug's softball skills, they ask him to pretend that he's a lawyer in order to play on their company team. Carrie worries that Doug won't be able to pull off being a lawyer, but he is so convincing, an opposing firm offers him a job. Meanwhile, after tracing his ancestry, Arthur believes his great-grandfather was a slave owner and makes it his own personal mission to correct things with Deacon on his ancestor's behalf.

A trip to a bed & breakfast becomes more than Doug and Carrie can handle. Meanwhile, Arthur has a romantic dilemma of his own.

The Heffernans hate an anniversary gift from the Palmers so much, they stage a robbery to rid themselves of it.

In order to afford a cruise, Doug convinces Carrie to cut her hair to sell to a wig maker, but regrets his idea after the deed is done.

Doug's lie to get Carrie to let him ride a rollercoaster at an amusement park blows up in his face. Meanwhile, Arthur lets Deacon shuttle him around in a wheelchair so they can jump to the front of the park's lines and Danny and Spence search for girls to pick up.

Doug and Carrie invite Ray and Debra Barone over for dinner.

Doug vows to lose 30 pounds.

Doug becomes jealous when Carrie makes the mistake of telling him she finds Deacon attractive; The gang go paintballing to celebrate Deacon's birthday, which turns into a war of jealousy.

Doug and Carrie meet the neighbors after a hurricane destroys both of their backyards. Carrie breaks their hearts by telling the truth and rejects the idea of a combined backyard. So the neighbors retaliate by disrupting their privacy by making an aboveground pool in a small space. But as Carrie tries to mount a lawsuit, Doug can't deny the temptation and joins the other side. But before the pool goes down, Carrie takes a quick swim and later, Doug tries to enjoy the lawn sprinkler.

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.

Against Carrie's commands, Doug takes $100 from the "emergency fund jar" to bet on a boxing match. When he and Deacon win $5,000, Doug realizes he can't let Carrie know he won big or she'll realize he stole the money. Deacon and Doug set out to burn it all off in a day of luxury spending. Meanwhile, Carrie is offered a job from the owner of the firm and when she finally works up the nerve to give notice, the offer ends up not being as firm as she thought.

Doug breaks the bed, and when Carrie and Doug find a new one that they like, it has to be ordered, thus leaving them with nothing, until they borrow two twin beds for the time being. Quickly the two realize that having their own space at night is making major improvements in their marriage. Arthur discovers that their sweet neighbor, Lou Ferrigno, is actually quite a gossip, when he overhears him through a peep hole in the basement that looks right into his yard. Arthur makes it his mission not to get tangled up in that mess by protecting what information Lou gets.