The Donnellys are four young, working-class Irish brothers involved in New York City's organized crime. Detectives investigate Joey Ice Cream, a life-long friend of the Donnellys who introduces the four brothers, setting the scene for the series.

Kevin Donnelly feels that he's on a hot streak, but when his gambling begins to add up, the eldest Donnelly brother, Jimmy, is forced to kidnap the bookie that Kevin owes money to. When the news of the kidnapping spreads around the neighborhood, connecting the Donnellys to the incident, the youngest brother, Sean, pays the price for having the Donnelly name. Meanwhile, Tommy Donnelly, the most reliable of the brothers, has to sacrifice for his family when Jimmy's plan lands Sean in the hospital.

While the Donnellys await on word surrounding Sean's condition, Jimmy sits in a police holding cell. Tommy and Kevin have trouble accepting their role in what happened as they sit at Sean's bedside. Tommy turns to longtime friend Jenny Reilly for support, leading to their relationship growing to one that's more than just friends. Meanwhile, the brothers ultimately tie up loose ends and pay their debt to the mob. Elsewhere, Nicky Cottero gains control of the Italian mob.

Tommy is visiting Jimmy in Jail but the visit turns quickly in a fight between both of them when Jimmy starts to think that Tommy doesn't want to help him. Meanwhile, Kevin goes after the witness who saw Jimmy stealing the truck full of shirts.

A guilt-ridden Tommy is shocked when Kate, Huey's widow, asks him to hold Huey's wake at the Firecracker. At the wake, the brothers discover that their taps are dry, which sends Kevin and Joey Ice Cream out to find alcohol. However, the best they can come up with is kosher wine. Jimmy arrives to pay his respects and Dokey begins to think that Huey may have beenhuged by Jimmy, leading to a standoff.

Tommy is hit with the hard realization that the Italian mob boss, Nicky Cottero, is not one to mess with when he threatens the brothers' mother, Helen. When Tommy runs out of options, he opts to take Dokey's bribe and steals the box that Dokey wants while visiting Huey's widow. Jimmy and Joey Ice Cream find Louie Downtown's cell phone and start to collect his payments after they find out he was behind a major gambling circuit. Meanwhile, Sean is able to come home from the hospital and Jenny has to face Tommy after sleeping with Samson.

Tommy gets thrust into Jimmy and Kevin's bookmaking when one of his friends, Maxwell, is about to get punished for not paying up. Tommy decides to track down the money, but ultimately is forced to do the punishing. Jimmy has Kevin get rid of Louie Downtown's cell phone and they meet up with Whitey who helps them transfer all of the numbers. However, a glimpse into the future reveals trouble ahead. Meanwhile, Jenny discovers her father's medical condition when she looks into why the diner's deposits haven't gone into the bank.

While Tommy and Kevin are collecting payments, Jimmy is painting the bar and tries to protect Sean from the business. Meanwhile, Kevin get a flashback from his childhood who makes him believe that he's truly lucky as a gambler and Jenny tries to watch over her ailing father while struggling to maintain the family's diner.

Tommy helps a woman who wants to get rid of the drug dealers in her apartment building, but ends up finding that doing so will be harder than he thought. Meanwhile, Jimmy tries to take over the neighborhood, but hits an all-time low when he has to get a payment from Jenny. Elsewhere, Nicky finds out the truth behind what really happened to Louie Downtown.

Tommy is finally able to do the only thing he wants to do, art. With the help of Kate, he gets a job at an art studio. But when he thinks he's now able to separate himself from the "business" of his family, he learns that it won't happen. Nicky, who decided not tohug Kevin, wants to use Louie Downtown's cell phone and offers a partnership to the Donnellys but will only deal with Tommy.

The loyalty of the brothers is put to the test and they have to kiss up to Dokey. Dokey puts them to the test, wanting them to clear an apartment building. The task proves more difficult then the boys thought it would be. Meanwhile things with Whitey come to a head.

In an effort to help save the diner from being repossessed by some mysterious person, Tommy searches for answers to find out who is buying up all the land in the area, and learns more about the circumstances of his fathers passing.

Jimmy wants a bigger piece of the earnings and asks Dokey to do so, but first he must complete another job for him. Tommy, Kevin and Joey help reappraise Reilly's diner while at the same time, Tommy tries to find out who cuddled his father. Jenny finds closure concerning her missing husband.

Tommy decides to leave town with his family fearing for their safety. Jenny finally deals with Samson while Nicky handles Alo for the last time. After much convincing, Jimmy decides to leave with his family.