The fourth season of It's Always Sunny in Philadelphia, premiered on FX on September 18, 2008. The season contains 13 episodes and concluded airing on November 20, 2008.
Charlie and Dee have been stealing Frank's delicious meats, so Frank leaves out human meat to get back at them. Driven by their cannibalistic needs, Charlie and Dee go in search of human flesh. Mac and Dennis harass Frank for hunting defenseless animals and think it would be much more badass to hunt something that could fight back ... like a human.
Charlie, Mac, and Dennis formulate a plan to take advantage of the rising gas prices. By purchasing excess amounts now, they can sell it in the future and profit. As usual, things don't go as planned. Dee is also out to make money when she learns that Bruce is going to give the family fortune to a Muslim cultural center. She and Frank try to stop him and get the cash for themselves.
Due to the gang's latest "business expenses," Paddy's is in dire need of money. Frank buys a billboard to advertise the bar, but Dee decides to create a viral video to post on YouTube for promotion. Charlie quickly joins her, leaving Frank and Mac to hold a contest for some hot models to feature on the billboard. Naturally, Dennis joins the competition to prove his worth.
Charlie finds out that the waitress has been seeing someone. He calls on Mac, his so-called best friend, to find out more information about the guy and to beat him up. However, it turns out that Mac is the guy the waitress has supposedly been seeing. Dennis, heartbroken that he's not Charlie's best friend, tries to win him over.
Part 1 of 2. Mac and Charlie fake their deaths to avoid the wrath of Mac's father who was released from prison and is out for vengeance.
Part 2 of 2. Dennis, Frank, and Dee find unique ways of coping with the apparent loss of their friends.
Charlie and Frank awake to find poop in their bed. Neither will confess to being the owner, so they, Mac, and Dennis try to scientifically deduce who dropped the deuce. Dee wants to do something a bit more sophisticated, so she invites the waitress and Artemis to a girls' night out.
A newspaper critic is kidnapped by the gang after he calls Paddy's pub the worst bar in Philadelphia.
After discovering Dennis' erotic memoir, Mac and Frank attempt to make some money off of it. Meanwhile, Dee and Charlie decide to spend a day in each other's shoes.
After Dee suffers a heart attack, she and Dennis try to live a healthier lifestyle. Meanwhile, Charlie and Mac take corporate jobs to get health insurance.
The gang fudge history by claiming that Paddy's Pub was responsible for cracking the Liberty Bell in an attempt to turn their dive into a Philadelphia landmark.
Hoping to make their own dreams come true, the gang sets out to give an unexpected family an extreme home makeover.