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's karaoke performance gets him an e-mail stalker.

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.

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.

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.

Doug and his pals rent an apartment to use as a secret hang-out. Meanwhile, Carrie goes to great lengths to please her newest client, Kirstie Alley.

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.

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.

Doug and Carrie try to get the Russian workers to repair their house, by going to extreme lengths of giving them vodka.

On the way to a overeating support group, Doug notices an abusive relationship group, and decides to join them instead. Although, Carrie becomes suspicious when he not only gains weight, but begins to cower in her presence.

Carrie finds out that while dating, Doug lied about getting a job to get her to sleep with him.

After Carrie accidentally injures Doug, he milks it to avoid distasteful tasks. Meanwhile, Arthur catches on to the ruse, and uses it to his advantage.

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

Doug panics when he starts getting sexy phone messages meant for another Doug Heffernan, but Carrie doesn't seem to care. Meanwhile, Danny tries to force a wedge between Spence and a new lady friend.

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

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

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.