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.

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 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.

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.

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 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.

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.

Doug's parents visit while Carrie's on a business trip and take over running the house, making Doug feel like a kid again. Also, Arthur tries to strike it rich by inventing a new type of screwdriver called "the Arthur's head."

Doug and Carrie are having fun on their vacation with their neighbors in St. Croix, but once Arthur calls with a quote on the current mold problem in the house, all is not so fun.

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.

Doug gets annoyed with Carrie when she loses her job and, rather than looking for employment, becomes extremely unmotivated. When Doug confronts Carrie about her laziness, she gets upset, claiming that she is simply trying to find herself. Carrie then enlists the help of Arthur and opens up her own company making decorative cell phone covers. However, when she invites her friends over to buy some of the covers, she realizes a new line of work might be in order.

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.

Doug and Deacon's relationship hits a speed bump when Deacon unknowingly befriends Doug's grade school archenemy.

Doug and Carrie are roped into helping out at their church during the holidays: he guards the manger, while she tries to bake a cake. Also, Arthur and Spence attempt to write a Christmas song so they can cash in on the holiday.

Bed bugs brought home by Arthur from a vacation force Doug and Carrie out of the house while a creepy exterminator does his job. Meanwhile, Spence and Danny argue over where to go for vacation.

Doug crashes Carrie's weekend company retreat, not realizing she's blown it off for a relaxing day with her girlfriends. Meanwhile, Danny and Spence pose as staff to sneak into a Huey Lewis concert.

After he sets a fire in the basement, Carrie decides it's time for Arthur to enter a retirement home, but Doug makes a discovery that makes him want to change Carrie's mind. Danny and Spence have a face-off over an agreement to swap bedrooms.