The film begins with Finbar "Barry" McMullen (Edward Burns) standing at the grave of his recently deceased father, along with his mother, who tells him that she's returning to her native Ireland to be with Finbar O'Shaughnessy (after whom Barry is named), her sweetheart of long ago. She tells Barry that while she gave Barry's father 35 of the best years of her life, she's going to start living life her way with the man she really loves. While this could be interpreted as disrespect for the memory of the family patriarch, it is later revealed in the movie that he was an alcoholic and abused his family prior to his death. It also provides a backdrop on why the three sons have relationship issues.
Flashing forward five years later, Barry's older brother Jack (Jack Mulcahy) has purchased their parents' Long Island home and lives in it with his wife Molly (Connie Britton), who is pressing Jack to start a family due to Her just turning 30 but he is reluct because of finances and worries about being a father given their father's failings. Jack is bothered by a conversation around commitment and never having another lover for life. He get involved with Ann (Elizabeth Makay), a former romantic interest of Barry's who pursues him as she likes relationships without the romantic entanglements and favours the term doing it over making love.
Meanwhile, Barry and the youngest brother, Pat (Mike McGlone) ask to temporarily move in with Jack, to which he reluctantly agrees. Pat and Barry, like their brother, are basically overgrown teenagers torn between prolonged adolescence and commitment to their girlfriends. Pat plans to break his engagement to Susan (Shari Albert) based on Barry's advice after she suggests they get married. Pat is upset when she breaks up with him first citing his indecisiveness about their relationship and the problems that could come between two faiths, as Susan is Jewish and Pat is a devout Irish Catholic. Pat has just finished college and has no idea what he wants to with his life whereas Susan and her father have his future fully laid out.
Barry has no interest in a long-term relationship, until he meets Audrey (Maxine Bahns), a woman whom he accuses of "stealing" an apartment that he was trying to rent by getting there first. Though things do not go well between them at first, they warm up to one another when they get set up on a blind date by a mutual friend and start a relationship.
Molly learns of Jack's affair after finding an unused condom in his pants as she is cleaning up after him one day. She confronts Jack, but he refuses to discuss it. His brothers also try to intervene, but to no avail as he tells them, that by Catholic tradition, no one can intervene in a married couple's disputes. Pat provides him good advice and counsel on fixing his relationship with Molly.
Pat approaches Susan to take him back but when she starts making life and career plans for him he decides to end the relationship for good. Moving back into the family home Pat has renewed a friendship with Leslie, a girl-next-door type who likes to work on her father's car and ended her engagement on her wedding day and gave up her religion. Pat was interested in her at school but she was dating the boy she became engaged to and her never had a chance to ask her out. The friendship develops into something a little more when they decide to head out to California together in a classic car that Leslie has her eye on.
Jack, Under the weight of guilt, finally breaks it off for good with Ann. He then returns home determined to rebuild his damaged marriage. On St Patrick's day he pays a visit to his father's grave, promising (in a voice-over) that he will be a better husband to his wife than his father was, emptying a flask of Irish whiskey over the grave.
Barry struggles with his career and opportunity to go to Hollywood with his script and his commitment to Audrey and breaks off their relationship. Pat again, as the younger brother, gives Barry good advice about not blowing the relationship as it might not come round again. Audrey decides to move home and at the last moment after she's walked out and returned his ring Barry has a change of heart and goes after her. The movie ends with all three brothers gathering at the family homestead with a newfound belief in love and a desire to not miss out on their chances like their mother had done.