Dennis, Dee and Mac find a baby in a Dumpster, and Dee and Mac decide to raise him. They also decide to use him to raise some cash. Meanwhile, Dennis joins an environmental-activist group, and isn't exactly welcomed with open arms. But he finds a way to take revenge. And Charlie wants Frank to take a DNA test to determine whether they're father and son. Frank won't do that, but he's happy to join Charlie on Dumpster-diving expeditions.
Mac, Dennis and Dee try out for the Philadelphia Eagles, but seem more interested in outdoing each other. Also trying out for the team is Doyle McPoyle, a brother of the gang's archenemies, Ryan and Liam McPoyle. The entire McPoyle clan shows up to cheer Doyle on, which is not good news for fellow tailgaters Frank and Charlie.
Dennis and Dee's abrasive mother has died, and the bad news is that she stiffed them in her will, leaving all her money to her humanitarian paramour, Bruce Mathis. But at least Dennis got her house. It's a "party mansion," and that's how he intends to use it.
The McPoyles invade Paddy's and take the gang hostage, demanding $100,000, a gassed-up boat and a reversible Planet Hollywood jacket. Meanwhile, Frank is crawling through the ductwork above Paddy's, searching for his will, when Liam McPoyle turns up the heat.
Dee gets a rude awakening when she discovers that "Fatty Magoo," an overweight loser from her high-school class, is now a svelte, successful clothing-store owner. So Dee decides to design a dress for her, but Dennis decides that he's the better designer. He also knows that he has the charm to sell it to Fatty.
The gang declares war on a Korean restaurateur who threatens to bump Paddy's from its coveted and profitable spot on the city's annual pub crawl. Meanwhile, Dee is determined to hold a talent show, primarily because she wants to win it.
The gang agrees to sell Paddy's after getting an offer that's too good to turn down. Problem is, Dee and Charlie, who aren't partners, must get real jobs. Members of Frank's "gang," the Yellow Jacket Boys, are played by members of the doo-wop group The Mighty Echoes, who perform.
The gang want to become local celebrities, so Mac and Charlie create their own newscast on a public-access channel, while Dennis and Dee set out to make a splash on the club scene.
Dee dates a famous local rapper and it could turn out to be true love, even though he might be mentally challenged. In any event, his success inspires Mac, Dennis, Charlie and Frank to start their own band.
Mac has been acting strangely, leading Frank, Dennis and Dee to believe that he's the serial killer who has been terrorizing Philadelphia. So they set out to catch him, but for Dennis and Dee, that means they must first learn to think like serial killers themselves. Frank, meanwhile, is content to let a chainsaw do his thinking for him.
Dennis is mistaken for a recently released child molester; Mac tries to bond with his ex-con father, who can't take his eyes off a creeped-out Dee; and Frank moves out of the apartment he's been sharing with Charlie, and moves in with Charlie's mother.
A misunderstanding with the mob over a set of speakers and a stash of cocaine prompts Dennis to hire himself out as a male escort. It's that, or he and the rest of the gang will get whacked.
A now-homeless Father Mara is employed to sell drugs on the street while Dennis embarks on life as a gigolo; and Mac tries to join the mob.
To rid their neighborhood of undesirables, Mac and Dee become vigilantes, and Frank and Dennis impersonate police officers. They enjoy the feeling of power this gives them...perhaps too much.
Season 3 ends as Charlie inadvertently puts Paddy's up as the grand prize in a dance marathon. The gang must then win the competition to keep the bar.
